What is a catch-all email address?
A catch-all (or wildcard) email address accepts all messages sent to any address at a domain, regardless of whether that specific address exists. For example, if example.com has a catch-all configured, emails to anything@example.com, xyz123@example.com, or made-up@example.com all get delivered. Catch-all is used by businesses to ensure no emails are lost due to typos, but it also means email verification tools cannot reliably determine if a specific address is real.
Why does catch-all matter for email marketing?
When a domain has catch-all enabled, email validation tools cannot confirm whether a specific address (like john@example.com) actually belongs to a real person. The validation tool sends a test connection to the mail server asking if the address exists, and the catch-all server says yes for any address. This means your email list may contain non-existent addresses at catch-all domains that will eventually bounce. Email marketers typically flag catch-all addresses as 'risky' — valid enough to attempt delivery but not guaranteed to be real.
How is catch-all detected?
The reliable way to detect catch-all is to attempt an SMTP conversation with the mail server using a randomly generated, clearly non-existent address (like xqz9random@domain.com). If the server accepts it (returns 250 OK), the domain is catch-all. If it rejects it (returns 550 or 554), it's not. This requires establishing an actual SMTP connection to the mail server. Some large email providers (Google Workspace, Microsoft 365) block this kind of verification at the server level regardless of catch-all status.
Should I remove catch-all addresses from my list?
It depends on your sending reputation and list quality goals. Hard-bouncing addresses at catch-all domains isn't possible until you actually send to them. Aggressive list managers remove all catch-all addresses to protect sender reputation. A more measured approach is to treat them as 'risky' — send once and remove if they hard bounce. For cold email campaigns, removing catch-all addresses is generally recommended. For transactional email to known users, you can send to them and let bounce tracking handle removals.