Cold email glossary

Short, plain definitions of the terms behind cold email deliverability. Each one says how the thing works, what goes wrong and what to do, and links to a free tool you can use right now.

• BIMI (Brand Indicators for Message Identification)BIMI lets some mailbox providers show your brand logo next to your emails, if your domain has strong DMARC and a valid logo file.
• Bounce rateBounce rate is the share of sent emails that could not be delivered, shown as a percent of all emails you sent.
• Bulk sender requirements (Gmail and Yahoo)Gmail and Yahoo require SPF, DKIM, DMARC, one-click unsubscribe and a spam rate under 0.3 percent from bulk senders since February 2024.
• Catch-all domainA catch-all domain accepts mail for any address at that domain, so verification cannot tell whether a specific mailbox really exists.
• Custom tracking domainA custom tracking domain is a subdomain of your own, such as track.yourdomain.com, used for open and click tracking links in your emails.
• Daily sending limitA daily sending limit is the most emails one mailbox should send in a day, set by the provider's rules and by what is safe for its reputation.
• Disposable email addressA disposable email address is a temporary address from a throwaway service that expires quickly and is not worth adding to a cold list.
• DKIM (DomainKeys Identified Mail)DKIM adds a digital signature to each email so the receiver can check that the message came from your domain and was not changed.
• DMARC (Domain-based Message Authentication, Reporting and Conformance)DMARC is a DNS policy that tells receivers what to do with mail that fails SPF and DKIM checks, and where to send reports about it.
• DMARC alignmentDMARC alignment means the domain that passed SPF or DKIM matches the domain in the visible From address of the email.
• Email blocklist (DNSBL)An email blocklist is a public list of IP addresses or domains linked to spam, which mail servers check to decide if they should reject your email.
• Email sequenceAn email sequence is a planned series of emails sent to one prospect with waits between steps, which stops when the person replies.
• Email verificationEmail verification checks whether an address is likely to accept mail before you send, to lower your bounce rate.
• Email warmupEmail warmup is the slow build-up of sending volume and engagement on a new mailbox so providers learn to trust it before you send cold email.
• Follow-up emailA follow-up email is a later step in a cold email sequence that adds a new point or a simple question to the first message.
• Hard bounceA hard bounce is a permanent delivery failure, such as an address that does not exist, and you should never email that address again.
• Inbox placementInbox placement is where a delivered email lands in the recipient's account: the main inbox, a tab such as Promotions, or the spam folder.
• Inbox rotationInbox rotation spreads one campaign over several mailboxes, so no single mailbox sends more than its daily limit.
• MTA-STSMTA-STS is a policy that tells other mail servers to use encrypted TLS when they deliver mail to your domain.
• MX recordAn MX record is a DNS entry that says which mail servers receive email for a domain, in order of priority.
• One-click unsubscribeOne-click unsubscribe adds two email headers that let a mailbox provider unsubscribe a person with a single click, as RFC 8058 describes.
• Open rateOpen rate is the share of emails that were opened, measured with a hidden tracking image, and it is no longer a reliable number.
• Personalization variables (merge tags)Personalization variables are placeholders such as a first name that your sending tool replaces with each contact's own data.
• PTR record (reverse DNS)A PTR record maps an IP address back to a hostname, and receivers use it to check that the sending server is who it claims to be.
• Reply rateReply rate is the share of your cold emails that get a reply, and it is the most honest success measure for cold email.
• Role-based email addressA role-based email address names a job or team, such as info@ or sales@, and usually reaches a shared inbox instead of one person.
• Secondary domainA secondary domain is a separate domain used only for cold email, so that any reputation damage stays away from your main business domain.
• Sender reputationSender reputation is the trust score a mailbox provider gives your domain and IP address, based on how recipients and servers react to your mail.
• Soft bounceA soft bounce is a temporary delivery failure, such as a full mailbox or a busy server, where the message may still be delivered later.
• Spam complaint rateSpam complaint rate is the share of delivered emails that recipients mark as spam, and Gmail wants it to stay below 0.3 percent.
• Spam trapA spam trap is an email address that real people do not use, kept by providers and blocklists to catch senders with poor list habits.
• SPF (Sender Policy Framework)SPF is a DNS record that lists which servers may send email for your domain, so receivers can spot forged mail.
• SpintaxSpintax is a text format where each curly-bracket group lists options, and the sender picks one at random for every email.
• Suppression listA suppression list holds addresses and domains you must never email, such as unsubscribes, hard bounces, complaints and customers.