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Email glossary: email terms explained A to Z

57 email terms in plain English, from BCC to BIMI. Each one links to a full guide or a free tool.

A

Alias: An extra address that delivers to the same inbox, such as [email protected] or [email protected]. Read more
Attachment: A file sent along with an email. Most providers limit attachments to about 20 to 25 MB. Read more
Authentication: Proof that an email really comes from the domain it claims, using SPF, DKIM and DMARC. Read more
Auto-reply: An automatic response, such as an out-of-office message. It is not a bounce. Read more

BCC: Blind carbon copy: recipients who get the email without the others seeing their address. Read more
BIMI: Brand Indicators for Message Identification: a standard that shows a verified brand logo next to authenticated email. Read more
Blocklist: A list of IP addresses or domains known for sending spam, used by mail servers to refuse mail. Also called a blacklist. Read more
Bounce: A message returned as undeliverable, with a code explaining why. Try the tool
Bounce rate: The share of sent emails that bounce. Keeping it under about 2% protects a sender's reputation. Read more
Business email: An address at your own domain, such as [email protected]. Read more

Catch-all: A domain that accepts mail for any address, real or not, so a checker can't tell whether a specific mailbox exists. Read more
CC: Carbon copy: extra recipients who can see each other's addresses. Read more
Cold email: A first email to someone you have no prior relationship with, usually for sales. Read more
Contact group: A saved list of addresses you can email all at once. Called a group in Outlook and a label in Gmail. Read more

Deliverability: How reliably your email reaches the inbox instead of the spam folder. Read more
Disposable email: A temporary address from a throwaway service that stops working after minutes or days. Read more
DKIM: DomainKeys Identified Mail: a digital signature added to email that proves it came from your domain and wasn't changed. Try the tool
DMARC: A DNS record that tells receivers what to do with email that fails SPF and DKIM for your domain, and sends you reports. Try the tool
DNS: The Domain Name System: the internet's address book, where a domain's email settings (MX, SPF, DKIM, DMARC) are stored. Try the tool
Domain: The part of an email address after the @, such as gmail.com or yourcompany.com. Read more
Double opt-in: Asking new subscribers to confirm by clicking a link in an email, which keeps fake and mistyped addresses off a list. Read more

Email client: An app for reading email, such as Outlook, Apple Mail or Thunderbird. Read more
Email header: The hidden part of an email that records its route and security checks. Try the tool
Encryption: Scrambling an email so only the intended reader can open it. Read more
ESP: Email service provider: a company that sends bulk or marketing email, such as Mailchimp or SendGrid. Read more

Greylisting: An anti-spam method where a server refuses the first attempt from a new sender; real servers retry and get through. Try the tool

Hard bounce: A permanent delivery failure, such as an address that doesn't exist. Read more

IMAP: A protocol that keeps your email on the server and syncs it across all your devices. Read more
Inbox: The folder where new, accepted email arrives. Read more

Label: Gmail's version of folders. One email can have several labels. Read more
List hygiene: Regularly removing bad, bouncing and inactive addresses from a mailing list. Read more
List-Unsubscribe: A header that lets people unsubscribe with one click from their email app. Required for bulk senders to Gmail and Yahoo. Read more

MX record: The DNS record that says which server receives email for a domain. Try the tool

Phishing: A fake email designed to steal passwords, money or personal information. Read more
Plus addressing: Adding +something before the @ ([email protected]) to create a free alias. Read more
POP3: An older protocol that downloads email to one device, often removing it from the server. Read more
PTR record: Reverse DNS: links a sending IP address back to a hostname. Missing PTR records cause rejections. Try the tool

Reply-To: A header that sends replies to a different address than the From address. Try the tool
Return-Path: The address where bounces are sent. It often differs from the From address when an email service sends for you. Try the tool
Role address: A shared address for a job rather than a person, such as info@, sales@ or support@. Read more

S/MIME: A standard for signing and encrypting email using certificates, built into Outlook and Apple Mail. Read more
Sender reputation: How trustworthy mailbox providers think a sending domain or IP is, based on its history. Read more
Signature: The block of text, usually with your name and contact details, added to the end of your emails. Read more
SMTP: Simple Mail Transfer Protocol: the system servers use to send email to each other. Read more
Soft bounce: A temporary delivery failure, such as a full mailbox. Read more
Spam: Unwanted bulk email. Also the folder where filtered mail goes. Read more
Spam trap: An address used only to catch spammers. Sending to one hurts your reputation. Read more
SPF: Sender Policy Framework: a DNS record listing the servers allowed to send email for your domain. Try the tool
Spoofing: Forging the From address so an email looks like it came from someone else. Read more
Subdomain: A domain under your main one, such as mail.yourcompany.com, often used to separate marketing email. Read more
Suppression list: A list of addresses an email service will never send to again, such as hard bounces and unsubscribes. Read more

TLS: Transport Layer Security: encryption that protects email while it travels between servers. Read more
TXT record: A DNS record that holds text, used for SPF, DKIM and DMARC. Try the tool

Verification: Checking whether an email address is correct and can receive mail, before you send to it. Read more

Warm-up: Slowly increasing how much a new domain or IP sends, so providers learn to trust it. Read more
Webmail: Reading email in a web browser instead of an app. Read more