Classic ASP e-mail verify that e-mail exists

Question

Here's something I couldn't find an answer to. Say you have a form and on that form you have a field for someone to enter their e-mail address. Now after the e-mail address is entered, is there a way after using RegEx to verify that it follows the syntax of an e-mail address, to then verify that it is a valid e-mail that can receive messages? I looked all over the net and found a deprecated way to do it that has since been stopped by patches, so I was wondering if there wasn't a way to do it on the server maybe polling the smtp server or something.

Answer 1

If you're looking to verify that the user hasn't made a mistake (or is giving you a bogus address because they aren't interested in your messages), you should probably do what every other system does: don't activate the account (or whatever) until you get some verification that the user has gotten the email by clicking a link or entering a code that the email contains.

You need to do this because you might never get an indication that an email address is invalid - some servers are configured to throw away some (or all) invalid email addresses or dump them in a spam bin. Just because the email appears to have been successfully sent doesn't mean it's valid or that it's getting to the right person.