Erik Aigner asked:
I was wondering how to distinguish inbound from outbound SMTP transactions.
Normally this would be a straightforward question, however my SMTP server has to handle a special case:
- Other domains might point to my MX domain (mail address aliases)
What outbound criteria should I check for?
Is it as simple as checking if the transaction is authenticated (via the AUTH command), or do any other rules apply (derived from the FROM/RCPT addresses)?
I guess alias addresses can be detected by resolving their MX?
If the sender is in your domain, it’s outbound.
If the recipient is in your domain, it’s inbound.
If neither are in your domain, it’s relay, and drop it like a hot potato.
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.