What should I use for catch-all domain detection?

For catch-all domain detection (checking whether a domain accepts mail for any address), the safest/common approach is:

Recommended method

1. Send SMTP RCPT TO probes to a few random, non-existent addresses at the domain.
2. Compare the server’s response:
   • If it returns 250/accepts the recipient for random addresses, it may be catch-all.
   • If it returns 550/551/552 for invalid recipients, it’s likely not catch-all.
3. Use multiple random addresses and ideally more than one MX server, because behavior can vary.

Important caveats

• Many servers use greylisting, anti-abuse tarpits, or accept then bounce later, which can make results unreliable.
• Some domains are accept-all temporarily or only on certain MX hosts.
• A server accepting RCPT TO does not guarantee the mailbox exists; it only means the server is willing to accept delivery.

Practical tools/libraries

Depending on your language:

• Python: smtplib (basic), or mail validation libraries that include SMTP probing
• Node.js: nodemailer with SMTP connection features
• Go: net/smtp (though limited), or raw SMTP via net

Best practice

If you need this for list hygiene or signup validation, use it as a signal, not a definitive result. Combine with:

• MX lookup
• syntax validation
• DNS checks
• SMTP probe results
• optional email confirmation

If you want, I can also give you:

• a Python example for catch-all detection,
• a Node.js example, or
• a full validation flow that includes MX + SMTP probing.