Email: terms A to Z
Every business email term explained in plain English: SMTP, IMAP, SPF, DKIM, DMARC, deliverability, and more.
Business email has layers of technical vocabulary, especially around deliverability, security, and configuration. This page is your reference for every term you'll encounter.
A to C
| Term | Plain-English definition |
|---|---|
| Alias | An additional email address that delivers to an existing inbox. E.g. hello@yourcompany.com forwarding to sarah@yourcompany.com. See Email aliases & forwarding explained. |
| Archive | A searchable store of old email messages. Some organizations are legally required to archive emails for a period of time. |
| Auto-reply | An automatic message sent in response to incoming email, e.g. "Thanks for your email, I'll respond within 24 hours." |
| Blacklist | A list of email servers or domains known to send spam. If your domain gets blacklisted, your emails may be blocked or sent to junk. |
| Bounce | When an email cannot be delivered and is returned to the sender. A hard bounce means the address doesn't exist; a soft bounce is a temporary issue (e.g. full inbox). |
| Catch-all address | An email address that receives messages sent to any nonexistent address at your domain, so nothing gets lost. |
| CC | Carbon copy. Sends a copy of an email to additional recipients who can see each other's names. |
| Client | Short for email client: the app or program you use to read and send email (Outlook, Apple Mail, Gmail in a browser). |
D to I
| Term | Plain-English definition |
|---|---|
| Deliverability | How reliably your emails reach recipients' inboxes (rather than spam folders). Affected by SPF, DKIM, DMARC, and sending reputation. See Why your emails land in spam (deliverability). |
| Distribution list | A group email address that delivers to a list of recipients. Useful for team-wide announcements. See Group & distribution lists explained. |
| DKIM | DomainKeys Identified Mail. A digital signature added to outgoing emails proving they genuinely came from your domain. See SPF, DKIM & DMARC for email senders. |
| DMARC | Domain-based Message Authentication, Reporting & Conformance. A policy that tells receiving servers what to do with emails that fail SPF or DKIM checks. |
| Domain | The part of an email address after the @. In sarah@yourcompany.com, the domain is yourcompany.com. |
| Encryption | Scrambling email content so only the intended recipient can read it. TLS encryption protects emails in transit. |
| Forwarding | Automatically sending copies of received emails to another address. |
| Google Workspace | Google's paid suite of business tools that includes Gmail with a custom domain. See What is Google Workspace?. |
| Header | Hidden technical metadata in an email that shows its routing path, authentication results, and timestamps. Useful for diagnosing delivery problems. |
| IMAP | Internet Message Access Protocol. The protocol that lets email clients sync messages from a mail server, so your emails stay on the server and appear across all your devices. |
| Inbox | The folder where received emails land. |
SPF and DKIM are two separate checks on the same email: one on the sending server, one on the signature. DMARC is not a third check: it is the policy that tells receiving servers what to do with emails that fail SPF or DKIM.
Read this as text
An email arrives claiming to be from your domain. The receiving mail server runs two checks on it. SPF checks the envelope: is this mail server on the approved list? DKIM checks the letter: was this email signed by the claimed domain, and is the signature still intact?
If both checks pass, the email has been authenticated and there is nothing for your DMARC policy to act on. Authentication on its own is not a promise of the inbox: spam filters also weigh things like your message content.
If either check fails, your DMARC policy tells the receiving server what to do. A policy of none delivers the email anyway and sends reports to you as the domain owner. Quarantine puts it in the spam or junk folder. Reject blocks it entirely, so it never reaches the recipient.
J to O
| Term | Plain-English definition |
|---|---|
| Junk folder | See Spam folder. |
| Mail server | A computer that sends, receives, and stores email on behalf of your domain. |
| Marketing email | Promotional email sent to lists: newsletters, campaigns, offers. Should go through dedicated platforms like Mailchimp or Klaviyo. See Transactional vs marketing email. |
| Microsoft 365 | Microsoft's paid suite that includes Outlook with a custom domain. See What is Microsoft 365?. |
| MX record | Mail Exchange DNS record. Tells the internet which mail server handles email for your domain. See DNS records explained. |
| Out-of-office reply | An automatic message sent when you're away, telling senders when you'll be back. See Out-of-office & auto-replies. |
P to R
| Term | Plain-English definition |
|---|---|
| Phishing | A fraudulent email that pretends to be from a trusted company or person, attempting to steal login details or money. See How to recognize a phishing email. |
| POP3 | Post Office Protocol 3. An older protocol that downloads emails to one device and, by default, removes them from the server. Less common now: IMAP is preferred. |
| Reply-to address | A different address that replies go to, even if the email was sent from another address. Common in marketing campaigns. |
| Reputation | The trustworthiness score of your sending domain and mail server in the eyes of email providers. High reputation = better deliverability. |
S to Z
| Term | Plain-English definition |
|---|---|
| Sender score | A numerical rating of your sending reputation, produced by a third-party monitoring service. Treat it as an indicator rather than the verdict. Each mailbox provider judges senders its own way. |
| Shared mailbox | An inbox multiple people can access and send from, e.g. support@yourcompany.com. See Shared mailboxes (like support@) explained. |
| Signature | Automatic text appended to the bottom of every email: name, title, phone, website. See Creating a professional email signature. |
| SMTP | Simple Mail Transfer Protocol. The standard protocol for sending email between servers (and from apps to your mail server). See What is SMTP (and why your site needs it)?. |
| Spam | Unsolicited bulk email. Also the folder where suspected junk email lands. |
| SPF | Sender Policy Framework. A DNS record that lists which servers are authorized to send email from your domain. See SPF records, explained. |
| TLS | Transport Layer Security. Encryption that protects emails while they're being transmitted between servers. |
| Transactional email | Automated email triggered by a user action: order confirmation, password reset, account notification. Should use dedicated SMTP services like SendGrid or Postmark. |
| Unsubscribe | The process a recipient uses to stop receiving marketing email. In the US, the CAN-SPAM Act requires marketing email to carry a clear, easy way to opt out, and opt-outs to be honored within 10 business days. Many other countries have similar rules. |
| Webmail | Accessing your email through a web browser instead of an installed app. See Accessing email on the web. |
| Whitelist | A list of senders whose emails should always be delivered (never filtered as spam). Also called a safe senders list. |
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