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
Assuming it's the user's address, some mail servers do allow the SMTP VRFY command to actually verify the email address against its mailboxes. Most of the major site won't give you much information; the gmail response is "if you try to mail it, we'll try to deliver it" or something clever like that.