Re^4: Determine if domain is actually used for email

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

Comment on Re^4: Determine if domain is actually used for email

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Re^5: Determine if domain is actually used for email by Your Mother (Archbishop) on Oct 04, 2011 at 19:35 UTC
Good to know. Thanks. "Safe bet" still sounds like gambling. :P	[reply]
Re^6: Determine if domain is actually used for email by vit (Friar) on Oct 05, 2011 at 13:08 UTC
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]
Re^7: Determine if domain is actually used for email by MidLifeXis (Monsignor) on Oct 05, 2011 at 13:21 UTC
Depends how many servers you are looking at and how good the IDS is on the site. If it was enough of a problem, I could see using that fingerprint to tag a site to watch behavior more closely. ISTR discussions about this many years ago on SPAM-L. Perhaps browsing the archives for doorknocking, testing addresses, and some similar search terms might be useful. --MidLifeXis	[reply]