Accept-All Domain
A domain configured to accept email sent to any local-part address, making individual mailbox verification impossible via SMTP alone.
An accept-all domain (also known as a catch-all domain) is configured so that its mail server accepts incoming email addressed to any local-part — meaning emails to random-string@domain.com and real-user@domain.com both receive a 250 OK response during SMTP verification. This makes it impossible to determine through SMTP alone whether a specific mailbox is real.
Prevalence and impact: Accept-all domains account for approximately 10-20% of B2B email addresses. Many companies use accept-all configurations for legitimate reasons: catching typos, ensuring no emails are missed, or routing all inbound mail through a central processing system. However, for email marketers, accept-all addresses represent a verification blind spot.
How SendSure resolves accept-all addresses: Rather than simply flagging them as "unknown" like many competitors, SendSure applies AI-powered catch-all resolution using a 54,000+ name database, external signals (Gravatar, GitHub, HIBP, Gmail API lookups), and machine learning scoring to estimate the probability that each accept-all address belongs to a real person. This produces actionable classifications like ACCEPT_ALL_VALID and ACCEPT_ALL_INVALID, letting you confidently include or exclude these addresses from your campaigns.
Related Terms
Catch-All (Accept-All)
A domain configured to accept emails sent to any address, regardless of whether the specific mailbox exists.
Email Verification
The process of confirming whether an email address is valid, deliverable, and belongs to a real person.
SMTP Handshake
The process of connecting to a mail server to verify if a specific mailbox exists, without actually sending an email.
Want to learn more?
Read our in-depth blog posts on email verification and deliverability.