Cold email glossary
Plain-English definitions of every cold email and deliverability term you'll come across — SPF, DKIM, DMARC, warmup, bounce types, sender reputation, RFC 8058, and more.
Cold email
An unsolicited email to a prospect with no prior relationship. Legal under CAN-SPAM (US) and GDPR (EU) for legitimate B2B purposes with a working unsubscribe and the sender's postal address.
Email warmup
Gradually increasing a mailbox's sending volume over 1-4 weeks so mailbox providers build trust in it. Bulk Email Boxer runs a 14-day automated warmup ramping from 5 to 500 emails/day.
SPF
Sender Policy Framework — a DNS TXT record listing which IPs may send mail for your domain. Combined with DKIM and DMARC to prevent spoofing.
DKIM
DomainKeys Identified Mail — a cryptographic signature on every email verifying it came from your domain unaltered. Required by Gmail and Yahoo for bulk senders since 2024.
DMARC
A DNS record telling receivers what to do with mail failing SPF/DKIM (none, quarantine, reject) and where to send authentication reports. Recommended policy for cold senders: p=quarantine.
Soft bounce
A temporary delivery failure (mailbox full, server busy). Retried with backoff. Signaled by 4xx SMTP codes.
Hard bounce
A permanent delivery failure (mailbox doesn't exist). Must be suppressed immediately; retrying hurts reputation. Hard-bounce rate above 2% triggers blocklisting.
Spam trap
An address operated by a provider or anti-spam org to detect poor list hygiene. Hitting even a few tanks domain reputation for months.
Catch-all
A domain that accepts mail for any address, making SMTP-level verification unreliable. Bulk Email Boxer's verifier flags catch-all domains.
Disposable email
A throwaway address (mailinator.com, 10minutemail.com) used to bypass signup verification. Flagged at verification time.
Role-based email
An address for a job function (info@, admin@, sales@) rather than a person — low engagement, often a distribution list. Best filtered out before sending.
List-Unsubscribe (RFC 8058)
Two email headers enabling one-click unsubscribe in Gmail/Yahoo, required for bulk senders since February 2024. Bulk Email Boxer stamps both on every send.
Sender reputation
An aggregate trust score providers maintain per sending domain and IP, driven by bounce rate, complaint rate, spam-trap hits, engagement, and authentication.
Domain reputation
Sender reputation scoped to your domain, independent of IP. The primary trust signal in 2026; persists across IP changes.
Bounce rate
Percentage of sent emails that bounce. Keep under 2%. Sustained hard bounces above 0.5% gets you flagged.
Open rate
Percentage of recipients who loaded the tracking pixel. Inflated by Apple Mail Privacy Protection, which pre-fetches pixels for Apple Mail users.
Reply rate
Percentage of recipients who replied — the only engagement signal providers fully trust in 2026. 5%+ is the floor for sustainable cold email; below 3% reputation trends down.
Apple MPP
Apple Mail Privacy Protection — pre-fetches all tracking pixels for Apple Mail users regardless of actual opens, reporting ~100% open rates and polluting the metric.
DNS
Domain Name System — translates domain names to IPs and stores email-routing metadata (MX, SPF, DKIM, DMARC). Cold-email deliverability depends on correct DNS.
MX record
A DNS record pointing to the mail server(s) that receive email for a domain. Missing or invalid MX records cause hard bounces.
Sequence
A series of automated cold emails over time (typically 3-7 messages, 3-5 days apart). Bulk Email Boxer supports branching on reply and A/B variants per step.
A/B testing
Sending variants of an email step to split portions of your list and comparing reply rates. Bulk Email Boxer supports up to 26 variants per step.
Spintax
Syntax for randomizing content with {option1|option2} placeholders so each email looks slightly different to spam filters.
Suppression list
Addresses that must never receive mail: hard bounces, unsubscribers, complaints, GDPR erasures. Bulk Email Boxer maintains this automatically per workspace.
CAN-SPAM
US law governing commercial email: no false headers, valid postal address, working opt-out processed within 10 business days. Penalties up to $51,744 per violation.
GDPR
EU regulation governing personal-data processing. For cold B2B email, 'legitimate interest' is a recognized lawful basis. Requires data export and right-to-erasure.