Email verification glossary
Plain-English definitions of the email verification and deliverability terms developers run into — from catch-all domains to SPF, DKIM, and spam traps.
Accept-all domain
An accept-all domain — another name for a catch-all domain — is configured to accept email sent to any address, including ones that don't exist.
Catch-all email
A catch-all (or accept-all) domain is configured to accept email sent to any address at that domain, including mailboxes that don't exist.
Disposable email
A disposable email address (DEA) is a temporary, throwaway mailbox — from services like Mailinator or 10MinuteMail — that a user creates to receive a confirmation without revealing their real address.
DKIM
DKIM (DomainKeys Identified Mail) is an email authentication standard that attaches a cryptographic signature to each message.
DMARC
DMARC (Domain-based Message Authentication, Reporting and Conformance) is an email authentication policy that builds on SPF and DKIM.
Double opt-in
Double opt-in is a subscription process where, after someone submits their email, you send a confirmation link they must click before being added to your list.
Email blocklist
An email blocklist (historically called a blacklist) is a database of IP addresses and domains identified as sources of spam.
Email bounce rate
Email bounce rate is the percentage of sent messages that were returned as undeliverable.
Email deliverability
Email deliverability is the measure of how reliably your messages reach recipients' inboxes rather than being blocked or filtered to spam.
Email list hygiene
Email list hygiene is the ongoing practice of keeping your subscriber list clean — removing invalid, inactive, disposable, and risky addresses — so your campaigns reach real, engaged recipients and your sender reputation stays healthy..
Email ping
An email ping is the informal name for the SMTP probe used to check whether a mailbox exists — connecting to the mail server and issuing a RCPT TO command without ever sending a message.
Email syntax validation
Email syntax validation checks that an address is correctly formatted according to the RFC 5322 standard — the right structure of local part, @ symbol, and domain.
Free email provider
A free email provider — such as Gmail, Outlook.com, Yahoo, or iCloud — offers personal email mailboxes at no cost on a shared domain.
Greylisting
Greylisting is an anti-spam technique where a mail server temporarily rejects messages from senders it doesn't recognize, returning a 'try again later' response.
Hard bounce
A hard bounce is a permanent email delivery failure caused by an invalid, non-existent, or blocked recipient address.
MX record
An MX (Mail Exchange) record is a DNS entry that specifies which mail server is responsible for receiving email for a domain.
Role-based email
A role-based email address is tied to a job function or department rather than an individual — for example info@, support@, sales@, or admin@.
Sender reputation
Sender reputation is a trust score that mailbox providers assign to your sending IP and domain based on your sending history.
SMTP verification
SMTP verification confirms whether an email mailbox exists by opening a connection to the recipient's mail server and starting — but never completing — a message delivery.
Soft bounce
A soft bounce is a temporary email delivery failure where the recipient address is valid but the message can't be delivered right now — for example because the mailbox is full or the server is temporarily unavailable.
Spam trap
A spam trap is an email address created or repurposed by mailbox providers and anti-spam organizations specifically to catch senders with poor list practices.
SPF
SPF (Sender Policy Framework) is an email authentication method that lets a domain publish, in DNS, the list of servers authorized to send mail on its behalf.
Verification vs. validation
Email validation checks whether an address is correctly formatted; email verification goes further and confirms the address can actually receive mail by checking the domain, MX records, and mailbox.
Put the theory to work
Mailbeam runs every one of these checks in a single API call. Start with 1,000 free verifications per month — no credit card required.