Plain-English explanations of the words used on this site. Each one says what the word means and why it matters for your email.
Stands for: Address.
What it is: A DNS record that links a name to an IPv4 address (a server's number on the internet).
What it does: It tells browsers and other servers which server to contact for that name. Websites use A records. In an SPF record, the word a means "the server my A record points to may send email".
Example: example.co.uk → 192.0.2.10.
Related words: AAAA record, IP address, DNS record
Stands for: Not an abbreviation. It is called "quad A" because IPv6 addresses are 4 times as long as IPv4 addresses.
What it is: The same as an A record, but for an IPv6 address (the newer, longer kind of address).
What it does: It tells browsers and other servers which IPv6 address to contact for that name. Many domains have both an A record and an AAAA record.
Example: example.co.uk → 2001:db8::10.
Related words: A record, IP address
Stands for: Brand Indicators for Message Identification.
What it is: A TXT record that points to your logo, so it can appear next to your emails in some mail apps, such as Gmail, Apple Mail and Yahoo.
What it does: It makes your real email easier to recognise. It only works when your DMARC policy is quarantine or reject, and Gmail and Apple Mail also need a paid certificate that proves you own the logo. The record is stored at default._bimi.yourdomain.
Related words: DMARC policy
What it is: A public list of server addresses that have recently sent spam. Also called a DNSBL (DNS-based blocklist) or blacklist.
What it does: Many mail servers check these lists before accepting email. If your mail server is listed, your email may be rejected or put in the spam folder. Common lists are Spamhaus, SpamCop and Barracuda.
Related words: IP address, Spam folder (junk)
What it is: An email that comes back to the sender because it could not be delivered, with an error message explaining why.
What it does: It tells you the email did not arrive. A "hard bounce" is permanent, for example the address does not exist. A "soft bounce" is temporary, for example the mailbox is full. Bounces are sent to the Return-Path address.
Related words: Return-Path, MX record
Stands for: Canonical Name (canonical means "the official one").
What it is: A DNS record that says "this name is another name for that name".
What it does: It sends anyone who looks up the first name to the second name. Microsoft 365 uses CNAME records to set up DKIM, so Microsoft can keep the keys up to date for you.
Example: www.example.co.uk → example.co.uk.
Related words: DNS record
Stands for: DomainKeys Identified Mail.
What it is: A hidden digital signature that your email service adds to every email you send.
What it does: Receiving mail servers check the signature against a public key in your DNS. If it matches, they know the email really came from your domain and was not changed on the way. This makes your email more trusted and helps it pass DMARC.
Related words: DKIM selector, DKIM public key, CNAME record, TXT record
Stands for: Domain-based Message Authentication, Reporting and Conformance.
What it is: A TXT record at _dmarc.yourdomain with your rules for email that claims to be from your domain.
What it does: It tells other mail servers what to do with email that uses your domain but fails the SPF and DKIM checks: deliver it, put it in spam, or refuse it. It can also ask them to send you reports. DMARC is what actually stops other people sending fake email as you.
Example: v=DMARC1; p=reject; rua=mailto:dmarc@example.co.uk
Related words: DMARC policy, DMARC alignment, DMARC reports, Spoofing, Phishing, SPF, DKIM
Stands for: Domain Name System.
What it is: The internet's address book: a worldwide system of servers that stores information about every domain.
What it does: It turns names like example.co.uk into the information computers need, such as which server hosts the website and which server receives the email. Your domain's DNS is managed by one company, for example Cloudflare or the company you bought the domain from.
Related words: DNS record, DNS cache, DNS propagation, DNSSEC, Nameserver, TTL
What it is: Your name on the internet, rented each year from a domain registrar.
What it does: It is the part of your email address after the @ sign, and the address of your website. All your DNS records belong to it.
Example: example.co.uk in jack@example.co.uk.
Related words: Domain registrar, Subdomain, DNS
What it is: Whether your email reaches the inbox, instead of the spam folder or being rejected.
What it does: It decides whether people actually see your email. It depends mainly on SPF, DKIM and DMARC being set up correctly, your sender reputation, and whether your mail servers are on a blocklist.
Related words: Sender reputation, Spam folder, Blocklist
What it is: Automatically sending email that arrives at one address on to another address.
What it does: It lets you read email from several addresses in one place. Forwarded email often fails SPF, because the forwarding server is not on the original sender's list. DKIM usually still passes, which is one reason DKIM matters for DMARC.
What it is: The company that runs your mailboxes, for example Microsoft 365 or Google Workspace.
What it does: It sends and receives your email. Your MX records must point to it, and your SPF record must include it, or your email will not arrive or will go to spam.
Related words: MX record, SPF include
Stands for: Internet Protocol address.
What it is: The number that identifies a server on the internet.
What it does: Computers use it to find each other. Spam lists list IP addresses, and SPF records can approve them with ip4: or ip6:.
Example: 192.0.2.10 (IPv4), or a longer address with colons (IPv6).
What it is: A computer that sends and receives email for a domain. Also called an MTA (mail transfer agent).
What it does: It accepts email for your addresses and passes your outgoing email to other mail servers. Your MX records point to the mail servers that receive your email. If you use Microsoft 365 or Google Workspace, they run the mail servers for you.
Related words: MX record, SMTP, Email provider
Stands for: Mail Transfer Agent Strict Transport Security.
What it is: A setting that tells other mail servers they must use an encrypted connection (TLS) with a valid certificate when they deliver email to you.
What it does: It stops someone in the middle reading or redirecting email on its way to you. It needs a TXT record at _mta-sts.yourdomain and a small policy file on a web address at mta-sts.yourdomain. A related TXT record at _smtp._tls.yourdomain (called TLS-RPT) asks mail servers to send you reports about connection problems.
Related words: TLS, Mail server
Stands for: Mail Exchanger.
What it is: A DNS record that names the server that receives email for your domain.
What it does: When someone sends you an email, their mail server looks up your MX record to find out where to deliver it. Without a correct MX record, email sent to you is usually not delivered.
Example: 0 example-co-uk.mail.protection.outlook.com delivers your email to Microsoft 365.
Related words: MX priority, Null MX, Email provider, DNS record
What it is: The server that holds your domain's DNS records.
What it does: It answers every question about your domain's DNS. You choose your nameservers at the company you bought the domain from. Changing them, for example to Cloudflare's, moves your DNS to that company.
Related words: DNS
What it is: Scam email that pretends to be from someone you trust.
What it does: It tries to trick you into clicking a link, paying a fake invoice or giving away a password. Phishing often uses spoofing. SPF, DKIM and DMARC make it much harder for scammers to use your domain for this.
What it is: A hidden address on every email where bounces are sent. Also called the envelope sender or "MAIL FROM" address.
What it does: It tells mail servers where to send bounces. It is often different from the "From" address you see, for example when a newsletter tool sends for you. SPF checks the domain of the Return-Path, not the visible From address, which is why DMARC alignment is needed.
Related words: SPF, DMARC alignment, Bounce
Stands for: PTR stands for Pointer.
What it is: A record that links an IP address back to a name: the opposite of an A record.
What it does: Many mail servers check that a sending server's IP address has a reverse DNS name that matches, and distrust email from servers without one. It is set by whoever owns the IP address, usually your hosting company or email provider, not in your own domain's DNS.
Example: 192.0.2.10 → mail.example.co.uk.
Related words: IP address, A record, Mail server
What it is: A score that mail services such as Gmail and Outlook keep for your domain and your sending servers.
What it does: It decides how they treat your email. Spam complaints, bounces, failed SPF, DKIM or DMARC checks and blocklist entries lower it. A poor reputation sends your email to the spam folder.
Related words: Email deliverability, Blocklist
Stands for: Simple Mail Transfer Protocol.
What it is: The language mail servers use to send email to each other.
What it does: Every email you send travels from server to server using SMTP. Mail apps and websites also use it to hand email to your mail server.
Related words: Mail server, TLS
What it is: The folder where mail services put email they think is unwanted or fake.
What it does: It keeps suspicious email away from your inbox. Email that fails SPF, DKIM or DMARC, or comes from a server on a blocklist, is more likely to end up here.
Related words: Blocklist
Stands for: Sender Policy Framework.
What it is: A TXT record that lists every server and service allowed to send email as your domain.
What it does: When an email arrives, the receiving mail server checks whether the server that sent it is on your list. It always starts with v=spf1, and a domain must have only 1 SPF record.
Example: v=spf1 include:spf.protection.outlook.com -all
Related words: SPF include, SPF ending (-all, ~all, ?all), SPF lookup limit, TXT record, DMARC
What it is: Sending an email with a fake "From" address, so it looks like it came from someone else.
What it does: Scammers use it to make phishing email look trustworthy. Without DMARC, anyone can send email that shows your address. With a strict DMARC policy, mail servers refuse it.
What it is: A name inside your domain.
What it does: It lets you use separate addresses for separate things, such as a shop or a newsletter. You do not need to buy subdomains: you create them by adding DNS records.
Example: www.example.co.uk or shop.example.co.uk.
Related words: Domain
Stands for: Transport Layer Security.
What it is: Encryption for connections between computers. It is what puts the padlock in your browser's address bar.
What it does: It stops anyone in the middle reading or changing what is sent. Mail servers use it to encrypt email on its way between them. MTA-STS makes it required for email sent to you.
Stands for: Time To Live.
What it is: A number on every DNS record, in seconds.
What it does: It says how long other DNS services may keep a saved copy of the record before asking again. "Auto" in Cloudflare means 5 minutes. A longer TTL means changes take longer to show up.
Related words: DNS cache
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