GLOSSARY
Email terms without the guesswork
Short definitions for terminology used throughout howto.email. Follow a term for the full technical reference.
Alignment
For DMARC, whether the authenticated SPF or DKIM domain aligns with the visible From domain. Read more →
ARC
Authenticated Received Chain; preserves authentication assessment information across intermediaries. Read more →
DKIM
DomainKeys Identified Mail; a cryptographic signature applied to a message by a signing domain. Read more →
DMARC
A policy and reporting layer built on aligned SPF and/or DKIM authentication. Read more →
DSN
Delivery Status Notification; structured information about delivery success or failure. Read more →
EHLO
The ESMTP greeting a client uses to identify itself and discover server extensions. Read more →
Envelope sender
The SMTP MAIL FROM identity used for delivery status handling and SPF evaluation. Read more →
MTA
Mail Transfer Agent; software that transfers messages using SMTP. Read more →
MTA-STS
A domain policy that tells supporting senders to require valid TLS when delivering to listed MX hosts. Read more →
MX
DNS Mail Exchanger record identifying hosts that accept mail for a domain. Read more →
NDR
Non-delivery report; a message describing why delivery failed. Read more →
PTR
Reverse-DNS record mapping an IP address back to a hostname. Read more →
Selector
A DKIM label used to locate a signing domain’s public key in DNS. Read more →
Smarthost
An SMTP relay used by another system as its next hop for outbound delivery. Read more →
SPF
Sender Policy Framework; authorizes hosts to use a domain in the SMTP envelope identity. Read more →
STARTTLS
SMTP extension used to upgrade an existing connection to TLS. Read more →
TLS-RPT
SMTP TLS reporting, used to receive aggregate reports about transport-security failures. Read more →