Email glossary

Short explainers of email jargon: what DKIM is, how hard bounce differs from soft, why DMARC matters.

Authentication

Cryptographic signature on outgoing email proving the message came from the claimed domain.

DNS TXT record listing the IPs allowed to send email on behalf of your domain.

Policy telling recipients what to do with messages that fail SPF and DKIM checks.

Standard for displaying a brand logo next to your messages in email clients.

Header telling the recipient how to unsubscribe. Mandatory for marketing email since 2024.

Standard that forces TLS encryption on inbound SMTP traffic to your domain.

Temporary delivery failure — mailbox full, transient network issue, MX unreachable.

Permanent delivery failure — mailbox does not exist, domain does not exist, blocked.

List of addresses you must not send to — bouncers, unsubscribers, complainers.

When a recipient hits "Spam" in their mail client — that is a complaint, fed back to the ESP.