7

I'm looking for a Postfix configuration option like smtpd_enforce_tls but one that lets me enforce TLS selectively, depending on what domain the email is coming in from. I need to allow non-TLS incoming email from all but certain selected originating domains.

Is this possible? I know that it's simple to selectively enforce TLS on email going out from Postfix, but I'm talking about email coming in.

7

Yes, you can - with a little engineering :)

Since you say you want to enforce TLS based on sender domain, you add a check_sender_access restriction to your smtpd_sender_restrictions, like so:

smtpd_sender_restrictions = check_sender_access hash:/etc/postfix/enforced_tls

and in /etc/postfix/enforced_tls:

@example.org   reject_plaintext_session
@example.net   reject_plaintext_session

Don't forget to postmap the file, and reload postfix when you're done.

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  • The domain names should not start with a @ as caught by @Georgi. – mmalone Mar 16 '18 at 0:23
4

/etc/postfix/enforced_tls must be in this format:

example.org   reject_plaintext_session
example.net   reject_plaintext_session

refer to http://www.postfix.org/access.5.html

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0

I would even suggest a more restrictive version by also requiring a valid certificate from the sending server like this:

/etc/postfix/main.cf:

...
smtpd_tls_ask_ccert = yes
smtpd_sender_restrictions = check_sender_access hash:/etc/postfix/enfoced_tls
...

/etc/postfix/enforced_tls:

example.org     reject_plaintext_session, permit_tls_all_clientcerts, reject
example.net     reject_plaintext_session, permit_tls_all_clientcerts, reject

This should also reject the session when the certificate of the connecting server cannot be validated via the CAs in smtpd_tls_CAfile, which in this case can safely contain the system default CAs. Please correct me if I'm mistaken here.

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