How to check if an email address exists without sending an email?

Question

I have come across this PHP code to check email address using SMTP without sending an email.

Has anyone tried anything similar or does it work for you? Can you tell

Answer 1

The general answer is that you can not check if an email address exists event if you send an email to it: it could just go into a black hole.

That being said the method described there is quite effective. It is used in production code in ZoneCheck except that it uses RSET instead of QUIT.

Where user interaction with his mailbox is not overcostly many sites actually test that the mail arrive somewhere by sending a secret number that must be sent back to the emitter (either by going to a secret URL or sending back this secret number by email). Most mailing lists work like that.