4 ms·
"3. Mail Exchanger existence checks Again, due to the robustness principle, just because a host does not define MX records does not mean they can’t accept mail
by graylights 13y ago
"3. Mail Exchanger existence checks
Again, due to the robustness principle, just because a host does not define MX records does not mean they can’t accept mail. Mail servers will often fall-back to A records to try and deliver mail. That’s why we go one step further than just a DNS query, we ping the Mail Exchanger to make sure that it actually exists."
Plenty of boxes don't respond to pings (icmp). Can I assume you're doing a tcp scan on mail ports?
- old-gregg 13y ago> Can I assume you're doing a tcp scan on mail ports? Nope. We're an ESP ourselves. Mailgun has delivered (and accepted) many billions of emails since our launch a few years ago. We have a lot of data on 99.99% other ESPs in the world and the most common misspellings for them. We also have ESP-specific data on what kind of RFC-compliant email addresses they do not allow.