A DNS record listing which servers are allowed to send email using your domain.

A cryptographic signature that proves an email really came from your domain and was not altered on the way.

A policy telling receivers what to do when SPF and DKIM fail, plus a reporting channel back to you.

The rule that the domain SPF or DKIM passed for must match the domain your recipient actually sees.

A standard that displays your logo beside your emails in the inbox, once DMARC is enforcing.

A policy that forces encrypted delivery to your mail servers instead of letting it fall back to plaintext.

A DNS record that asks sending servers to report when they could not deliver to you over an encrypted connection.

A chain of signatures that lets a forwarder vouch for authentication results that forwarding would otherwise break.

Email addresses that exist only to catch senders who are not managing their lists properly.

Public lists of IPs and domains that receivers use to decide whether to accept your mail.

A receiver's running judgement of whether mail from you is wanted, built from behaviour over time.

Headers that give the mailbox its own unsubscribe button, so recipients leave your list without reporting you as spam.

The channels through which receivers tell you which recipients marked your mail as spam.

The systems that fetch every URL in your email before the recipient does — and score the destination.

DNS records saying which servers accept incoming mail for your domain.

A bounce is a delivery failure — permanent if the address does not exist, temporary if something is merely in the way.

Forty bounce codes explained — remove the address, retry, or fix your own side.

Layered systems that score a message on authentication, reputation, content and engagement before deciding where it lands.

The protocol every email travels over, and where most of the codes, limits and failures come from.

A mail server that accepts every address at the domain, so a verification check cannot tell a real mailbox from a made-up one.

How a verifier asks a mail server whether a mailbox exists — without sending anything — and what each answer means.

The handful of record types that between them decide whether your mail arrives.

Your own domain for click and open tracking links, instead of one shared with every other user of your sending tool.

Gradually increasing send volume from a new mailbox so receivers build a positive history before real campaigns start.

The PTR record that maps a sending IP back to a hostname — required by Gmail before it will accept mail from the IP.

The handful of patterns companies use to issue addresses, how common each is, and how to tell which one a company uses.