in reply to Re^2: Determine if domain is actually used for email
in thread Determine if domain is actually used for email

Sure... but unless I'm misled, with UDP there simply is no way to know for sure excepting an out of band response—a visit to a tokenized URI sent in a message or a return message from the same domain/address. So no checks will be guaranteed. "Heroic" messages to circumvent misused standards / client-fail seems a mistake.

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Re^4: Determine if domain is actually used for email
by Limbic~Region (Chancellor) on Oct 04, 2011 at 19:17 UTC
    Your Mother,
    I have no idea where UDP came into the conversation since SMTP is a TCP protocol. I agree that there is no way to be sure unless you can deliver mail to a recipient and get a DSN or, preferred, a response. Seeing if the server is listening on port 25 and is responding in a manner consistent with a SMTP server and not giving a 521 status code is a pretty safe bet though.

    Cheers - L~R

[reply]

      Good to know. Thanks. "Safe bet" still sounds like gambling. :P

[reply]
        Seeing if the server is listening on port 25 and is responding in a manner consistent with a SMTP server and not giving a 521 status code is a pretty safe bet though.

        So am I right that, although not 100% reliable, this might be a good way to check if a domain has an actual email with no risk to be caught as spammer? Is there a code which implements this approach?
[reply]

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