What is “accept-all” behavior and how should it be labeled?

When an email validation tool checks whether an address exists, it has a conversation with the receiving mail server. For most addresses, the server responds clearly: "yes, this mailbox exists" or "no, it doesn't." Accept-all (also called catch-all) is the case where the server responds "yes" to every single address at that domain, regardless of whether the individual mailbox is real.

From a validation standpoint, accept-all behavior makes it impossible to verify the address at the mailbox level. The server is configured to accept everything first and sort it out later (or silently discard it). That "yes" from validation means the domain is reachable, not that the address is deliverable.

How it should be labeled: "catch-all" or "unknown." Not "valid." An address at a catch-all domain passes the server-level check but can still generate a hard bounce when you actually try to deliver. Labeling it "valid" would overstate what you know.

Accept-all behavior is common on corporate domains, where IT teams configure mail servers to accept everything so that important messages don't bounce due to typos in the recipient's name. This is why B2B lists often have high catch-all rates. It doesn't mean the addresses are bad. It means you don't know.

What to do with catch-all addresses depends on your risk tolerance:

• Conservative approach: Don't send to catch-all addresses initially. Monitor engagement from your confirmed-valid sends and only add catch-alls after you have positive engagement signals.
• Pragmatic approach: Send to catch-alls but watch the bounce rate closely. If a catch-all address hard bounces, remove it immediately and update your record.

A good validation tool should flag catch-all addresses clearly so you can make this call rather than treating them as confirmed deliverable. If yours doesn't distinguish between "valid" and "catch-all," that's a gap worth addressing before your next large send.