0

Let's say i have these records:

  • A mail.somedomain: 127.0.0.1
  • A mail.mailserverdomain: 127.0.0.1
  • MX somedomain: mail.somedomain

A MTA connects mail.somedomain for delivering mail to somedomain and gets a certificate for mail.mailserverdomain presented, and the MTA presents its hostname as mail.mailserverdomain in HELO.

Is this a valid TLS session or would this mean a certificate for a wrong hostname (expecting somedomain or reverse.somedomain)?

Improve this question
0

1 Answer 1

Reset to default
2

Surprise! For a TLS negotiation with a mail server, typically the subject name is not checked at all. Much of the encryption between mail servers is entirely opportunistic, using only self-signed certificates, often with a subject name of localhost.

Unfortunately, it's not really possible to do much better than this, as it is possible to MitM the connection and prevent the encryption negotiation from ever taking place. And it's not possible to prevent that attack until DNSSEC (or an equivalent) is fully deployed and everyone requires proper certificates of everyone else. This is unlikely to happen before we retire.

If your email must be encrypted end to end, you'll need to do it yourself.

Improve this answer
1
  • Thank you, interesting link. And yeah, a sad state, but let's at least try to do it as good as possible.
    – allo
    Sep 20, 2016 at 16:04

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .