Email & DNS Glossary

Short, plain-English definitions of the terms that matter for business email hosting, deliverability and DNS configuration.

SPF (Sender Policy Framework)

SPF is a DNS record listing which servers may send email for a domain, helping receivers detect forged sender addresses.

SPF works by publishing a TXT record at your domain listing authorised sending servers (by IP address or by referencing another domain's SPF record via include:). When mail arrives claiming to be from your domain, the receiving server checks whether it came from one of those authorised sources.

Example record: v=spf1 include:_spf.example.com ~all

SPF alone doesn't stop spoofing — it's most effective combined with DMARC, which enforces what happens when SPF fails.

DKIM (DomainKeys Identified Mail)

DKIM cryptographically signs outgoing email so receiving servers can verify it wasn't altered, using a public key published in DNS.

Each outgoing message gets a digital signature generated with a private key your mail server holds. The corresponding public key is published as a DNS TXT record at {selector}._domainkey.yourdomain.com. Receiving servers fetch that public key and verify the signature matches.

DMARC (Domain-based Message Authentication, Reporting & Conformance)

DMARC tells mail servers what to do when a message fails SPF or DKIM, and reports back.

DMARC builds on SPF and DKIM by adding a policy (p=none, p=quarantine, or p=reject) that tells receivers how to handle mail that fails authentication, plus a reporting address where aggregate reports are sent.

Example record (monitor mode): v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com

MX Record (Mail Exchange Record)

An MX record is a DNS entry that specifies which mail server(s) should receive email for a domain, each with a priority number.

When another server wants to deliver mail to you@yourcompany.com, it looks up your domain's MX records to find where to send it. Multiple MX records can exist with different priority numbers — lower numbers are tried first.

DNS (Domain Name System)

DNS translates human-readable domain names into the technical records — like server addresses and mail routing — behind the internet.

DNS is often described as the internet's phone book, but for business email it's more than a lookup — the records themselves (MX, SPF, DKIM, DMARC, and more) carry the actual configuration that determines whether your mail is delivered and trusted.

SMTP (Simple Mail Transfer Protocol)

SMTP is the standard protocol used to send email between mail servers and from mail clients to a server.

SMTP handles the "sending" side of email — your mail client uses it to hand a message to your mail server, which then uses SMTP again to relay it toward the recipient's server. It's distinct from IMAP/POP3, which handle retrieving mail you've received, not sending it.

IMAP (Internet Message Access Protocol)

IMAP lets a mail client read mail stored on the server, keeping folders and read status in sync across devices.

With IMAP, your mail stays on the server and your device just displays a synced view of it — read a message on your phone, and it shows as read on your laptop too. This is why IMAP (not POP3) is the standard recommendation for anyone checking mail from more than one device.

POP3 (Post Office Protocol version 3)

POP3 downloads email to a single device, usually removing it from the server — unlike IMAP, which keeps everything synced.

POP3 is older and simpler than IMAP: it downloads mail to one device and, by default, doesn't keep it synced elsewhere. It still has narrow uses (e.g. a single archival device), but for most businesses checking mail across phone, laptop and webmail, IMAP is the better fit.

For deeper explanations of each term, see our blog articles on SPF, DKIM, DMARC and MX records. To check your own domain's configuration, visit our Free Tools page.