Glossary
Email verification terms, in plain words
Short definitions for the words you will see in results, docs and deliverability guides.
A to Z
All terms
30 terms. Pick a letter to jump to it.
Bounce rate
The share of sent emails that were rejected.
Read CCatch-all domain
A domain that accepts mail for every address.
Read DDisposable email
A temporary inbox that deletes itself.
Read DDKIM
A signature that proves an email was not changed.
Read DDMARC
A policy for mail that fails SPF and DKIM.
Read DDouble opt-in
A sign-up flow where a new subscriber must click a confirmation link before they are added to the list.
Read EEmail deliverability
How reliably your emails reach the inbox instead of bouncing or landing in spam.
Read EEmail syntax
The formatting rules an email address must follow, such as one @ sign, allowed characters and length limits.
Read EEmail validation
Checking that an email address is correctly formatted and points at a domain that can receive mail.
Read EEmail verification
Checking whether an email address can actually receive mail before you send to it.
Read EEmail warm-up
Gradually increasing the volume sent from a new domain, mailbox or IP so mailbox providers can build trust in it.
Read GGreylisting
An anti-spam method where a mail server temporarily refuses mail from an unfamiliar sender and accepts it on a later retry.
Read HHard bounce
A permanent rejection, like a missing mailbox.
Read LList decay
The gradual loss of working addresses from an email list as people move on and accounts close.
Read LList hygiene
The ongoing work of keeping an email list accurate by removing bad, risky and inactive addresses.
Read MMX record
The DNS record that says where mail is delivered.
Read NNull MX
A special MX record, defined in RFC 7505, that says a domain does not accept email.
Read PPlus addressing
Adding a +tag to the local part of an address, such as [email protected], so mail still reaches the main inbox.
Read PPTR record
A reverse DNS record that maps an IP address back to a hostname, used by mail servers to check who is connecting.
Read RRole-based email
An address for a team, like info@ or sales@.
Read SSecure email gateway
A filtering service that sits in front of a company's mailboxes and screens incoming mail for spam and threats.
Read SSender reputation
How inbox providers rate your sending domain.
Read SSMTP handshake
The opening exchange of commands between two mail servers, which verification tools use to ask whether a mailbox exists without sending a message.
Read SSMTP status codes
The numeric replies a mail server gives during delivery, which say whether a message was accepted, deferred or rejected and why.
Read SSoft bounce
A temporary rejection, like a full inbox.
Read SSpam complaint rate
The share of delivered emails that recipients mark as spam.
Read SSpam trap
An address used to catch senders with poor lists.
Read SSPF
A DNS record listing who may send for a domain.
Read SSuppression list
A list of addresses that are blocked from future sends, such as unsubscribes, hard bounces and spam complaints.
Read TTypo domain
A misspelled version of a real email domain, such as gmial.com for gmail.com, usually entered by mistake in a form.
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