Glossary
Cold outreach, in plain English.
Every term you need to evaluate a deliverability problem, write a sequence that lands, or argue with your IT team about DKIM. Bookmark this page.
Bounce rate
The percentage of sent emails that came back undelivered. Above 5% is a deliverability emergency.
Cold email (cold outreach)
Unsolicited 1:1 email sent to recipients you don't have an existing relationship with — typically for B2B sales or recruiting.
Complaint rate (spam rate)
The percentage of recipients who hit the "report spam" button. Even tiny rates matter — under 0.1%.
DKIM (DomainKeys Identified Mail)
A cryptographic signature added to every outbound email, verifiable against a public key in your DNS.
DMARC
A policy record that tells receivers what to do when SPF or DKIM fails — and reports back what happened.
Domain rotation
Sending high-volume cold outreach across multiple domains so no single domain crosses reputation thresholds.
Email warmup
The process of gradually ramping a new mailbox's sending volume to build sender reputation before production.
ESP (Email Service Provider)
The infrastructure provider that actually transmits your email. SendGrid, Amazon SES, Postmark, etc.
Feedback loop (FBL)
A formal channel through which mailbox providers send "this user complained" notifications back to the sender.
ICP (Ideal Customer Profile)
A defined set of attributes (industry, company size, role, geography, tech stack) that describes your best-fit prospects.
List-Unsubscribe header
An email header that gives mailbox providers a one-click way to unsubscribe — required by Gmail and Yahoo for senders over 5K/day.
Mailbox provider
The company that operates the inbox where your message lands — Google (Gmail / Google Apps), Microsoft (Outlook.com / M365), Yahoo, etc.
MTA (Mail Transfer Agent)
The server software that actually moves email between systems. Postfix, Exim, sendmail.
MX records
DNS entries that tell the world which servers receive email for your domain.
Open rate
The percentage of delivered emails that were opened. Less reliable than reply rate, but still the most-quoted top-of-funnel metric.
Reply rate
The percentage of sent emails that got a reply. The only metric in cold outreach that actually predicts revenue.
Sender reputation
A composite score mailbox providers maintain for every sending IP and domain — your invisible deliverability grade.
Sequence (cadence, drip)
A multi-touch outreach campaign — typically 3–8 messages spaced over 2–6 weeks — that auto-pauses when a recipient replies.
SPF (Sender Policy Framework)
A DNS TXT record listing which servers are allowed to send email on your domain's behalf.
Suppression list
A list of email addresses that should never be re-mailed — bounces, complaints, manual unsubscribes.
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