On 16/02/2021 21:34, Viktor Dukhovni wrote: >> On Feb 16, 2021, at 3:57 PM, Dominic Raferd <domi...@timedicer.co.uk> wrote: >> >>> In what way does that improve your security over the default, which >>> allows 1.0 and 1.1? >> As stated this is for auth clients i.e. our own people, using SMTPS or >> STARTTLS. There is no problem for us in enforcing it for them, they don't >> use old MTAs anyway and if they did this would force them to upgrade, which >> would be good. This also seems to be the OP's scenario (as his logs imply >> the problem comes from submission port i.e. 587). We use standard postfix >> settings for permitted protocols for outsider emails (port 25) because (as >> frequently advised here) lower security is better than no security at all. >> HTH > Yes, on the submission port, dropping support for TLS < 1.2 > is much more reasonable, because presumably you can make > informed judgements as to what software the authorised users > have at their disposal.
I was surprised by the level of disagreement on what best practice is. I spent a bit of time this afternoon rereading that part of the postconf manual. I thought I'd summarise what I've understood, both for other readers and to be contradicted if I've misunderstood. Setting these two should guarantee that no incoming connection is unencrypted. smtpd_use_tls = yes smtpd_tls_auth_only = yes But which versions? This seems to make sense: require high grade ciphers. But the man page makes a good argument for setting this to medium. I'd originally set smtpd_tls_mandatory_ciphers = high, I've switched it to medium. I had initially set smtpd_tls_exclude_ciphers = RC4, aNULL, but, again, I see the man page makes a good argument against that, so I've removed the exclusion. The default value of smtpd_tls_mandatory_protocols is !SSLv2, !SSLv3. The suggestion on this thread was to set it as follows, which was certainly better than what I had (an explicit inclusion rather than an explicit exclusion). I'm rather tempted, based on the man page, to change it to its default value (essentially, >= TLSv1). I'm open to argument. smtpd_tls_mandatory_ciphers = medium # smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1 smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3 -- Jeff Abrahamson +33 6 24 40 01 57 +44 7920 594 255 http://p27.eu/jeff/ http://mobilitains.fr/
