Glossary

Cold email glossary

Short definitions, each with why it matters when you send from your own inbox and where to read more.

Updated 1 October 2026 · By Otman Ounana · How we research

Each term has a one-sentence definition, a reason it matters, an example and links to the guides that go deeper.

In this section

• Approval queueAn approval queue is a screen where every drafted email waits for a person to read it and approve, edit or reject it before it can be sent.
• Bulk senderA bulk sender, in Google's definition, is any sender that sends close to 5,000 messages or more to personal Gmail accounts within a 24-hour period.
• CAN-SPAMCAN-SPAM is the United States federal law that sets rules for commercial email: no deceptive headers or subject lines, a physical postal address, and an opt-out that is honoured.
• CASLCASL is Canada's Anti-Spam Legislation, a consent-based law that prohibits sending a commercial electronic message unless the recipient has consented, expressly or by implication.
• Catch-all domainA catch-all domain is one whose mail server accepts messages for any address at that domain, whether or not a mailbox exists.
• Cold emailCold email is a first message to someone you have no existing relationship with, sent because their work looks relevant to what you offer.
• DKIMDKIM (DomainKeys Identified Mail) is a way for a sending server to sign each message with a private key, so the receiver can check the signature against a public key published in the sender's DNS.
• DMARCDMARC is a DNS record that tells receiving servers what to do with a message that fails SPF and DKIM checks for the domain in its From address, and where to send reports about it.
• DMARC alignmentDMARC alignment is the requirement that the domain in a message's visible From address matches the domain that passed the SPF or DKIM check.
• Double opt-inDouble opt-in is a sign-up process in which a person first asks to join a list and then confirms by clicking a link sent to their address.
• Follow-upA follow-up is a later email in the same thread, sent to someone who has not replied to the first.
• Hard bounceA hard bounce is a permanent delivery failure, such as an address that does not exist, which the receiving server reports with a 5xx status code.
• Legitimate interestLegitimate interest is one of the lawful bases for processing personal data under the GDPR, allowing processing that is necessary for a genuine interest of the organisation, provided the person's rights do not override it.
• List-UnsubscribeList-Unsubscribe is an email header that carries an unsubscribe address, so a mail app can show its own Unsubscribe button without the recipient opening the message.
• MX recordAn MX (mail exchanger) record is a DNS entry that names the servers which accept incoming mail for a domain.
• One-click unsubscribeOne-click unsubscribe is the standard, RFC 8058, that lets a mail app unsubscribe someone with a single automatic web request, so the recipient never sees a confirmation page or a login.
• Out-of-office replyAn out-of-office reply is an automatic message sent by someone's mail account to say that they are away.
• PECRPECR, the Privacy and Electronic Communications Regulations 2003, is the UK law that governs unsolicited electronic marketing, including email.
• Postmaster ToolsPostmaster Tools is a free Google service that shows a domain's owner how Gmail sees the mail it sends, including the rate at which recipients mark it as spam.
• Reply rateReply rate is the share of first emails that receive a reply from a real person, usually shown as a percentage of emails sent.
• Sender reputationSender reputation is the standing a mailbox provider gives a sender, built from how recipients and receiving servers have treated the sender's earlier mail.
• Soft bounceA soft bounce is a temporary delivery failure, such as a full mailbox or a busy server, reported with a 4xx status code or as a delayed delivery.
• Sole traderA sole trader is a self-employed person who runs a business in their own name, without forming a limited company.
• Spam trapA spam trap is an email address that real people do not use, kept by a mailbox provider or a blocklist operator to catch senders who mail addresses they should not.
• SPFSPF (Sender Policy Framework) is a DNS record in which a domain lists the mail servers allowed to send email for it.
• Suppression listA suppression list is the set of addresses you must never email again: people who opted out, addresses that hard-bounced and anyone else you have promised to leave alone.
• Warm-upWarm-up is the practice of starting with a low sending volume and raising it step by step, so mailbox providers see a steady pattern rather than a sudden burst.

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