Email deliverability glossary: every term outbound teams need to know
20 min read · 72 terms · Published March 2026 · Last updated March 27, 2026
Cold outreach has its own vocabulary. Half the terms get used interchangeably by people who should know better. This glossary defines every deliverability term that matters for outbound teams, in plain language, with context about why each one matters for your operation.
A
Authentication
The process of proving your emails are legitimately sent from your domain. Uses three protocols: SPF (who can send), DKIM (message integrity), and DMARC (policy enforcement). Required by Gmail and Microsoft for all senders doing volume.
Why it matters for cold outreach: Without authentication, cold emails are far more likely to land in spam or be rejected outright.
Read more: SPF, DKIM, and DMARC explained →Auto-pause
An automated protection mechanism that stops a mailbox or domain from sending when bounce rates or spam complaints approach ISP thresholds. The mailbox is paused before damage accumulates, preventing cascading reputation loss.
Why it matters for cold outreach: Without auto-pause, a single bad list segment can burn a domain before anyone notices.
Read more: Auto-healing docs →Auto-healing
The automated process of detecting damaged infrastructure, quarantining affected mailboxes, reducing volume, monitoring recovery, and gradually returning to full capacity. Also called the healing pipeline.
Why it matters for cold outreach: Manual recovery from domain damage takes weeks of careful attention. Automation makes it reliable and consistent.
Read more: Auto-healing docs →B
Blacklist
A database of IP addresses or domains identified as sources of spam. Maintained by organizations like Spamhaus, Barracuda, and SORBS. Being listed on a major blacklist can cause widespread delivery failures across all ISPs that reference that list.
Why it matters for cold outreach: Cold outreach domains with high bounce rates or spam complaints are at constant risk of blacklisting.
Read more: Deliverability troubleshooting →Bounce (Hard)
A permanent delivery failure. The email address does not exist, the domain is invalid, or the receiving server has permanently rejected the message (SMTP 5xx response). Hard bounces should never be retried.
Why it matters for cold outreach: Hard bounces directly damage sender reputation. Each one signals to ISPs that you are sending to bad addresses.
Read more: Bounce rate and deliverability →Bounce (Soft)
A temporary delivery failure. The mailbox is full (452), the server is temporarily unavailable (451), or the message exceeds size limits. Soft bounces are retried by the sending platform, usually 3-5 times over 24-72 hours.
Why it matters for cold outreach: Repeated soft bounces to the same address indicate a dead mailbox and should be treated as hard bounces after 3 failed attempts.
Read more: Bounce classification docs →Bounce (Transient)
A temporary, often infrastructure-related bounce caused by network issues, DNS resolution failures, or server rate limiting. Distinguished from soft bounces by being caused by sending-side or network issues rather than recipient-side problems.
Why it matters for cold outreach: Transient bounces usually resolve on retry and are less damaging than hard bounces, but clusters of them indicate infrastructure problems.
Read more: Bounce classification docs →Bounce Rate
The percentage of sent emails returned as undeliverable, calculated as bounced emails divided by total emails sent. Stored as a percentage from 0 to 100. The single most important metric for cold email infrastructure health.
Why it matters for cold outreach: Google flags senders above 2% bounce rate. Microsoft at 5%. Exceeding these thresholds triggers throttling or blocking.
Read more: Bounce rate thresholds →Bulk Sender
Google defines a bulk sender as anyone sending more than 5,000 messages per day to Gmail accounts. Bulk senders face stricter requirements including mandatory authentication, one-click unsubscribe, and bounce rate limits below 0.3% for spam complaints.
Why it matters for cold outreach: Most cold outreach teams hit bulk sender thresholds quickly when running multiple campaigns. The rules apply per sending domain.
Read more: Bounce rate thresholds →C
Campaign
A structured sequence of emails sent to a list of leads through a sending platform like Smartlead or Instantly. Contains email copy, scheduling rules, and lead assignments. Multiple campaigns can share mailboxes and domains.
Why it matters for cold outreach: Campaign-level bounce tracking helps identify which list segments or copy variations are causing deliverability problems.
Catch-all Domain
A domain configured to accept email sent to any address at that domain, regardless of whether the specific mailbox exists. The mail server responds with a 250 (success) status to every RCPT TO command during SMTP verification.
Why it matters for cold outreach: About 15-30% of B2B domains are catch-all. They are the single biggest source of surprise bounces in cold outreach because validation tools cannot confirm individual addresses.
Read more: Catch-all domains in cold outreach →Clay
A data enrichment platform used by outbound teams to find and enrich lead contact information. Clay aggregates data from multiple sources and can output enriched leads via webhooks to downstream tools.
Why it matters for cold outreach: Clay is the most popular enrichment source for cold outreach teams. Leads from Clay still need validation before sending because Clay does not verify email deliverability.
Read more: Clay integration docs →Compliance
Adherence to email sending regulations and ISP requirements. Includes CAN-SPAM, GDPR (for EU recipients), CASL (Canada), authentication standards, bounce rate limits, and unsubscribe requirements.
Why it matters for cold outreach: Non-compliance can result in legal penalties, blacklisting, and permanent loss of sending ability on a domain.
Cooldown
A period of zero or near-zero sending on a domain or mailbox that has been damaged. Typically 1-2 weeks. Allows ISP reputation signals to decay and the domain to shed negative associations before re-warmup begins.
Why it matters for cold outreach: Skipping cooldown and immediately re-warming a damaged domain usually fails. ISPs remember recent bad behavior.
Read more: Quarantine docs →Correlation Engine
A system that analyzes relationships between bounce patterns, list segments, campaigns, and infrastructure components to identify root causes of deliverability problems. Detects when bounces are concentrated on specific domains or list sources.
Why it matters for cold outreach: Without correlation analysis, teams often blame the wrong component when deliverability drops.
D
DKIM (DomainKeys Identified Mail)
An email authentication protocol that adds a cryptographic signature to outgoing messages. The receiving server uses a public key published in DNS to verify the signature, confirming the message was not altered in transit and was authorized by the sending domain.
Why it matters for cold outreach: DKIM is one of three required authentication protocols. Without it, ISPs treat your emails as potentially spoofed.
Read more: SPF, DKIM, and DMARC explained →DMARC (Domain-based Message Authentication, Reporting and Conformance)
A DNS-based policy that tells receiving mail servers what to do when SPF or DKIM checks fail. Options are none (monitor only), quarantine (send to spam), or reject (block entirely). Also generates aggregate reports showing authentication results.
Why it matters for cold outreach: Gmail and Microsoft require DMARC for bulk senders. Start with p=none for monitoring, then move to p=quarantine after confirming alignment.
Read more: SPF, DKIM, and DMARC explained →DNS (Domain Name System)
The distributed naming system that translates domain names to IP addresses and stores records that affect email delivery, including MX records (mail servers), SPF records (authorized senders), DKIM keys, and DMARC policies.
Why it matters for cold outreach: Misconfigured DNS is a common cause of deliverability failures. A missing or incorrect SPF record can cause all emails from a domain to fail authentication.
Domain
The part of an email address after the @ symbol (e.g., company.com). In cold outreach, teams typically use separate sending domains from their primary business domain to isolate reputation risk. Multiple mailboxes operate under one domain.
Why it matters for cold outreach: Domain reputation is shared across all mailboxes. One bad mailbox can damage every other mailbox on the same domain.
Read more: Domain warming methodology →Domain Burnout
When a sending domain accumulates enough negative signals (high bounce rates, spam complaints, blacklisting) that it becomes effectively unusable for cold outreach. Recovery may be possible but often takes longer than starting fresh.
Why it matters for cold outreach: Domain burnout is the costliest failure in cold outreach. Prevention through validation and monitoring is always cheaper than recovery.
Read more: Domain burned: recovery and prevention →Domain Warmup
The process of gradually increasing sending volume on a new domain over 4-6 weeks to build positive sender reputation with ISPs. Starts at 5-10 emails per day per mailbox and increases by 5-10 daily if bounce rates stay healthy.
Why it matters for cold outreach: Rushing warmup is one of the most common causes of domain burnout. Patience during warmup prevents months of problems later.
Read more: Domain warming methodology →Disposable Email
A temporary email address created through services like Guerrilla Mail, Temp Mail, or Mailinator. These addresses work for minutes or hours and then expire. They pass SMTP verification but are worthless for outreach.
Why it matters for cold outreach: Enrichment tools sometimes return disposable addresses, especially from web scraping sources. Sending to them wastes capacity and signals list quality problems.
Deliverability Protection Layer (DPL)
An infrastructure layer that sits between your lead data and your sending platform, providing validation, health scoring, bounce monitoring, auto-pause protection, and automated recovery. Superkabe is a DPL.
Why it matters for cold outreach: Most outbound stacks lack a DPL. Data goes directly from enrichment to sending with no quality gate or post-send monitoring.
Read more: Superkabe DPL overview →E
Email Validation
The comprehensive process of checking whether an email address is formatted correctly (syntax), has valid DNS records (MX lookup), exists at the server level (SMTP probe), and is safe to send to (catch-all, disposable, role-based, and spam trap checks).
Why it matters for cold outreach: Validation is the first and most important defense against bounces. It typically prevents 85-95% of hard bounces from bad addresses.
Read more: Email validation docs →Email Verification
A subset of email validation focused specifically on confirming a mailbox exists via SMTP handshake. Does not include catch-all detection, disposable filtering, or spam trap identification.
Why it matters for cold outreach: Verification alone is insufficient for cold outreach because it misses several categories of risky addresses.
Read more: Validation vs. verification →Engagement Rate
The percentage of recipients who interact with your emails through opens, clicks, or replies. ISPs use engagement signals to determine inbox placement. Higher engagement leads to better deliverability in a reinforcing cycle.
Why it matters for cold outreach: Low engagement rates signal to ISPs that your emails are unwanted. Cold outreach naturally has lower engagement than marketing email, making list quality even more important.
Execution Gate
A decision point in the lead processing pipeline where leads are evaluated against rules before being allowed to proceed to sending. Checks include validation status, health score, campaign capacity, and domain health.
Why it matters for cold outreach: The execution gate prevents leads from reaching campaigns when infrastructure conditions are not safe for sending.
Read more: Execution gate docs →F
Feedback Loop (FBL)
A mechanism where ISPs report spam complaints back to the sender. When a recipient marks your email as spam, the ISP sends a notification to the address specified in your email headers. Major ISPs like Yahoo, Outlook, and AOL operate feedback loops.
Why it matters for cold outreach: Feedback loop data is critical for identifying which campaigns or list segments generate complaints. Too many complaints trigger throttling or blocking.
G
Greylisting
A spam filtering technique where a mail server temporarily rejects emails from unknown sender-recipient pairs with a 451 response code. Legitimate mail servers retry after a delay (typically 5-30 minutes), while spam servers usually do not retry.
Why it matters for cold outreach: Greylisting causes temporary bounces on first contact with a recipient. If your sending platform does not retry properly, these become permanent failures.
Gmail Bulk Sender Rules
Requirements Google implemented in 2024 for senders delivering more than 5,000 messages per day to Gmail accounts. Mandate SPF, DKIM, and DMARC authentication, spam complaint rates below 0.3%, one-click unsubscribe support, and valid forward and reverse DNS.
Why it matters for cold outreach: These rules reshaped cold email operations. Authentication is no longer optional and complaint monitoring is mandatory.
Read more: Bounce rate thresholds →H
Hard Bounce
A permanent email delivery failure. The address does not exist (550), the domain is invalid, or the server has permanently refused the message. Hard bounces generate an NDR (Non-Delivery Report) and should never be retried.
Why it matters for cold outreach: Every hard bounce directly damages your sender reputation with ISPs. High hard bounce rates are the fastest way to burn a domain.
Read more: Bounce classification docs →Health Classification (GREEN / YELLOW / RED)
A traffic-light system for categorizing the health status of mailboxes, domains, and leads. GREEN means healthy and operating normally. YELLOW means at risk and requiring attention. RED means damaged and requiring immediate action or removal from active sending.
Why it matters for cold outreach: Health classification provides instant visibility into infrastructure status without requiring manual interpretation of bounce data.
Read more: Entity statuses docs →Health Gate
The first evaluation point for incoming leads. Examines validation results, email risk indicators, and domain characteristics to classify leads as GREEN (safe to route), YELLOW (route with caution), or RED (block from sending).
Why it matters for cold outreach: The health gate prevents bad leads from ever reaching your campaigns and damaging your infrastructure.
Healing Pipeline
An automated multi-phase recovery process for damaged infrastructure. Phases include quarantine (zero sending), cooldown (minimal sending), recovery (gradual volume increase), and return-to-active. Each phase has specific exit criteria.
Why it matters for cold outreach: Automated healing removes the human error factor from domain recovery. Manual recovery attempts often fail because operators increase volume too quickly.
Read more: Warmup and recovery docs →I
Inbox Placement
Whether an email lands in the recipient's primary inbox, promotions tab, spam folder, or is blocked entirely. Determined by the recipient's mail server based on sender reputation, authentication, content, and engagement history.
Why it matters for cold outreach: Inbox placement is the ultimate metric for cold outreach. An email that lands in spam is effectively undelivered regardless of what your sending platform reports.
Infrastructure Assessment
A comprehensive evaluation of your sending infrastructure covering domain authentication (SPF, DKIM, DMARC), mailbox health, bounce rates, sending patterns, and risk indicators. Produces a scored report with specific remediation steps.
Why it matters for cold outreach: Regular infrastructure assessments catch problems before they cause domain damage. Like a health checkup for your outbound operation.
Read more: Infrastructure assessment docs →ISP (Internet Service Provider)
In the email context, the organization that operates the receiving mail server. Major ISPs for B2B email include Google (Gmail/Workspace), Microsoft (Outlook/365), Yahoo, and corporate mail servers. Each ISP has different spam filtering rules and reputation thresholds.
Why it matters for cold outreach: Different ISPs have different bounce rate thresholds and reputation algorithms. What works for Microsoft may trigger blocks at Google.
L
Lead Routing
The process of assigning incoming leads to specific campaigns and mailboxes based on rules like persona match, minimum health score, campaign capacity, and domain health. Ensures leads reach the right campaign through the safest infrastructure.
Why it matters for cold outreach: Smart routing distributes risk across healthy infrastructure instead of overloading specific mailboxes or campaigns.
Lead Scoring
Assigning a numerical risk score to each lead based on email validation results, catch-all status, domain reputation, role-based detection, and other signals. Higher scores indicate safer leads. Used by the execution gate to make routing decisions.
Why it matters for cold outreach: Lead scoring lets you prioritize the safest leads for your best domains and handle riskier leads with more caution.
Read more: Risk scoring docs →Load Balancing
Distributing sending volume across multiple healthy mailboxes and domains to prevent any single mailbox from being overloaded. Takes into account mailbox health, daily sending limits, and domain-level capacity.
Why it matters for cold outreach: Without load balancing, hot mailboxes get more volume than they can handle safely, while healthy mailboxes sit idle.
Read more: Load balancing docs →M
Mailbox
An individual email account used for sending cold outreach (e.g., john@sendingdomain.com). Each mailbox has its own reputation with ISPs, sending limits, and health status. Multiple mailboxes typically operate under one domain.
Why it matters for cold outreach: Mailbox-level monitoring is essential because individual mailboxes can degrade independently even on a healthy domain.
Mailbox Fatigue
The gradual degradation of a mailbox's deliverability over time due to accumulated negative signals. Even at safe bounce rates, long-running high-volume mailboxes develop fatigue from hundreds of low-level negative signals.
Why it matters for cold outreach: Mailbox rotation and periodic rest periods prevent fatigue from gradually eroding deliverability.
Mailbox Rotation
The practice of cycling through multiple mailboxes across campaigns to distribute sending volume and prevent individual mailbox fatigue. Active mailboxes send while resting mailboxes recover reputation.
Why it matters for cold outreach: Rotation extends mailbox lifespan and prevents the gradual deliverability decay that comes from constant high-volume sending.
Read more: Mailbox rotation docs →MillionVerifier
An email verification service known for high accuracy and the lowest per-email cost in the market (approximately $0.29 per 1,000 verifications). Offers bulk verification, API access, and catch-all detection.
Why it matters for cold outreach: Superkabe uses MillionVerifier as its underlying verification engine, combining MV's accuracy with Superkabe's infrastructure protection layer.
MX Record
A DNS record type that specifies which mail servers are responsible for accepting email for a domain. MX records include a priority value — lower numbers indicate higher priority. If the primary server is unavailable, email is routed to backup servers.
Why it matters for cold outreach: Validating MX records is step two of email validation. No MX record means the domain cannot receive email.
Monitoring
Continuous tracking of email infrastructure metrics including bounce rates, delivery rates, engagement, spam complaints, blacklist status, and authentication health. Real-time monitoring enables proactive response before damage accumulates.
Why it matters for cold outreach: Most outbound teams only discover problems after domains are already damaged. Real-time monitoring is the difference between prevention and recovery.
Read more: Monitoring docs →O
Open Rate
The percentage of delivered emails that were opened by recipients. Measured via a tracking pixel. Less reliable since Apple Mail Privacy Protection (2021) pre-loads pixels, inflating open rates. Still useful as a relative metric between campaigns.
Why it matters for cold outreach: Declining open rates across campaigns can indicate deliverability problems — emails landing in spam report no opens.
Overloaded Mailbox
A mailbox sending at or above its safe daily capacity. Overloaded mailboxes are more likely to trigger ISP throttling because the sending pattern appears automated and high-volume.
Why it matters for cold outreach: Load balancing prevents overloading by distributing volume across available healthy mailboxes.
P
Paused (Status)
A mailbox or campaign status indicating sending has been stopped, either manually by the user or automatically by auto-pause protection. Paused mailboxes do not send but remain configured and can be reactivated.
Why it matters for cold outreach: Pausing before thresholds are breached prevents permanent damage. It is always better to pause and investigate than to keep sending into a problem.
Read more: Entity statuses docs →Platform Adapter
A software component that translates between Superkabe's internal data format and a sending platform's API (Smartlead, Instantly, EmailBison). Handles authentication, rate limiting, data mapping, and error handling for each platform.
Why it matters for cold outreach: Platform adapters let Superkabe work with multiple sending platforms without requiring changes to your workflow.
Read more: Multi-platform sync docs →Priority Routing
A routing strategy that assigns the safest leads (highest validation scores) to your best-performing infrastructure (healthiest domains and mailboxes). Riskier leads go to more expendable infrastructure or are held for manual review.
Why it matters for cold outreach: Priority routing maximizes the value of your healthiest domains by protecting them from risky leads.
Q
Quarantine (Healing Phase)
The first phase of the healing pipeline. A damaged mailbox or domain is quarantined — completely removed from active sending for a defined period (typically 1-2 weeks) to allow negative reputation signals to decay.
Why it matters for cold outreach: Quarantine is the foundation of recovery. Attempting to recover without a cooldown period almost always fails.
Read more: Quarantine docs →R
Recovery Phase
The phase of the healing pipeline where a previously quarantined mailbox or domain gradually resumes sending. Volume increases slowly (5-10 emails/day increments) with continuous bounce monitoring. Any bounce spike triggers a return to cooldown.
Why it matters for cold outreach: Recovery requires patience and monitoring. Automated recovery phases prevent the common mistake of increasing volume too quickly.
Read more: Warmup and recovery docs →Resilience Score
A composite metric that measures how well your overall sending infrastructure can absorb problems without significant capacity loss. Factors include number of healthy domains, mailbox distribution, redundancy, and recovery pipeline status.
Why it matters for cold outreach: A high resilience score means one failed domain does not cripple your operation. Low resilience means you are one bad day from a capacity crisis.
Restricted Send
A mailbox status between healthy and paused. The mailbox can still send but at reduced volume (typically 50% of normal capacity). Used during recovery phases and when health indicators are trending negative but have not yet hit pause thresholds.
Why it matters for cold outreach: Restricted sending is a middle ground that keeps the mailbox active while reducing risk during marginal health conditions.
Risk-Aware Routing
A routing approach where lead assignment considers both the lead's risk score and the current health of available infrastructure. Risky leads are routed to more expendable infrastructure. Healthy infrastructure receives only verified-safe leads.
Why it matters for cold outreach: Risk-aware routing protects your best domains from your riskiest data, extending domain lifespan significantly.
Role-Based Email
An email address associated with a function rather than an individual (info@, sales@, support@, admin@, webmaster@). These addresses typically go to shared inboxes, have low engagement, and signal to ISPs that the sender is not targeting individuals.
Why it matters for cold outreach: Sending cold outreach to role-based addresses wastes capacity and can damage reputation. Most should be excluded from cold campaigns.
S
Sender Reputation
A score ISPs assign to sending domains and IP addresses based on historical bounce rates, spam complaints, engagement metrics, sending volume patterns, and blacklist status. Reputation determines whether your emails reach the inbox, land in spam, or are blocked.
Why it matters for cold outreach: Sender reputation is the single most important factor in cold email deliverability. Everything else — copy, timing, personalization — is irrelevant if your reputation is poor.
Read more: Email reputation lifecycle →Smartlead
A cold email sending platform that manages campaigns, mailbox rotation, and sequencing. Supports multiple mailboxes per campaign and offers API access for programmatic lead management and campaign control.
Why it matters for cold outreach: Smartlead is the most popular sending platform for cold outreach teams. It does not include built-in validation or infrastructure protection.
Read more: Smartlead integration docs →Soft Bounce
A temporary delivery failure caused by recipient-side issues: full mailbox (452), server temporarily unavailable (451), message too large, or rate limiting. Sending platforms typically retry soft bounces 3-5 times over 24-72 hours.
Why it matters for cold outreach: Soft bounces that persist across retries should be treated as hard bounces. Chronic soft bounces to the same addresses waste sending capacity.
Read more: Bounce classification docs →SPF (Sender Policy Framework)
A DNS record that lists which IP addresses and servers are authorized to send email on behalf of your domain. Receiving servers check the sending IP against the SPF record. If the IP is not listed, the email fails SPF authentication.
Why it matters for cold outreach: SPF is the first authentication check. It is the easiest to configure and the first thing to verify when debugging deliverability issues.
Read more: SPF, DKIM, and DMARC explained →Spam Complaint
When a recipient manually marks your email as spam in their email client. ISPs track complaint rates per sender domain. Gmail enforces a 0.3% complaint rate threshold for bulk senders.
Why it matters for cold outreach: Spam complaints are more damaging than bounces per incident. Even a small number of complaints can trigger throttling or blocking.
Spam Trap
An email address operated by ISPs or anti-spam organizations to identify senders with bad practices. Pristine traps are addresses that never belonged to a real person — hitting one proves you are using a scraped or purchased list. Recycled traps are abandoned real addresses reactivated as traps.
Why it matters for cold outreach: Hitting a spam trap can cause immediate blacklisting. Validation tools with trap databases can catch some, but not all, trap addresses.
Standby Mailbox
A warmed mailbox kept in reserve, not actively assigned to campaigns, ready to replace a mailbox that gets paused or enters the healing pipeline. Maintains sending readiness through low-volume warmup activity.
Why it matters for cold outreach: Standby mailboxes prevent capacity loss when active mailboxes need to be paused. They are your infrastructure insurance policy.
T
Throttling
When an ISP intentionally slows down email delivery from a specific sender by adding delays between message acceptance. Used as a warning signal before outright blocking. Indicates the ISP has detected concerning sending patterns.
Why it matters for cold outreach: Throttling is a warning. If you see delivery slowing down, immediately reduce volume and investigate. Continuing at full speed leads to blocking.
Transient Bounce
A temporary bounce caused by network issues, DNS resolution failures, or server-side rate limiting. Distinct from soft bounces (recipient-side) and hard bounces (permanent). Usually resolves on the next retry attempt.
Why it matters for cold outreach: Clusters of transient bounces indicate infrastructure problems on your end or your sending platform, not bad email addresses.
Read more: Bounce classification docs →V
Validation Score
A numerical score assigned to each email address based on the results of all validation checks. Factors include SMTP validity, catch-all status, domain age, role-based detection, and spam trap risk. Used by the execution gate to make routing decisions.
Why it matters for cold outreach: Validation scores provide a single metric for lead quality, making it easy to set thresholds for automatic routing vs. manual review.
Read more: Risk scoring docs →Validation Status
The outcome of email validation: valid (safe to send), invalid (do not send), catch-all (unverifiable — send with caution), disposable (do not send), role-based (exclude from cold outreach), or unknown (could not determine — investigate).
Why it matters for cold outreach: Each validation status requires a different handling strategy. Treating them all the same defeats the purpose of validation.
W
Warm Recovery
A recovery strategy for damaged domains that gradually increases sending volume while monitoring bounce rates. Typically starts at 5-10 emails per day after a quarantine period and increases by 5-10 daily if metrics stay healthy.
Why it matters for cold outreach: Warm recovery is slower than domain replacement but preserves existing domain reputation and authentication configuration.
Read more: Warmup and recovery docs →Warmup
The process of establishing sender reputation on a new mailbox or domain by gradually increasing sending volume over 4-6 weeks. Includes both warmup emails (sent to engaged recipients or warmup networks) and gradual introduction of cold outreach volume.
Why it matters for cold outreach: Every new domain and mailbox needs warmup before full-volume cold outreach. Skipping warmup is the second most common cause of domain damage after sending to unvalidated lists.
Read more: Domain warming methodology →Webhook
An HTTP callback that sends data from one system to another in real-time when an event occurs. In outbound infrastructure, webhooks connect enrichment tools (Clay) to validation services (Superkabe) to sending platforms (Smartlead).
Why it matters for cold outreach: Webhook-based lead flow enables fully automated pipelines from enrichment through validation to sending with zero manual intervention.
Frequently Asked Questions
What is the difference between a hard bounce and a soft bounce?
A hard bounce is permanent — the address does not exist or the server has permanently rejected your message. A soft bounce is temporary — full mailbox, server down, or message too large. Soft bounces are retried. Hard bounces should never be retried and the address should be removed immediately.
What is sender reputation and how does it affect cold email?
Sender reputation is a score ISPs assign to your domain and IP based on bounce rates, spam complaints, and engagement. Good reputation means inbox. Poor reputation means spam folder or blocks. Cold outreach domains are especially vulnerable because they are young and thin on positive signals.
What does DMARC do and is it required for cold email?
DMARC tells receiving servers what to do when SPF or DKIM checks fail. Since Gmail's 2024 bulk sender rules, DMARC is effectively required for any sender doing volume. Without it, your emails are more likely to be filtered or rejected.
How long does domain warmup take?
4-6 weeks for cold outreach domains. Start at 5-10 emails per mailbox per day and gradually increase. Most domains reach 30-50 emails per mailbox per day within 4 weeks if bounce rates stay healthy. Rushing warmup is one of the most common causes of domain damage.
What is a catch-all domain and how do I handle them?
A catch-all domain accepts email to any address, making verification unreliable. 15-30% of B2B domains are catch-all. Options: send at reduced priority, exclude entirely, or send only to addresses with additional validity signals like LinkedIn profile matches.
What is the difference between email validation and email verification?
Verification confirms a mailbox exists via SMTP. Validation is broader: verification plus catch-all detection, disposable filtering, role-based identification, and spam trap detection. Cold outreach needs full validation.
What is a spam trap and how do I avoid hitting one?
Spam traps are addresses operated by ISPs to catch bad senders. Never use purchased lists, validate all addresses, re-validate lists older than 30 days, and use a validation tool with spam trap detection.
What is greylisting and how does it cause bounces?
Greylisting temporarily rejects emails from unknown senders, expecting legitimate servers to retry. If your sending platform does not retry properly, the email bounces permanently. This is a sending infrastructure issue, not a validation failure.
Know the terms. Protect your infrastructure.
Superkabe monitors every metric in this glossary in real-time. Validation, bounce tracking, health classification, auto-pause, and healing — all automated.