Security concern over default smtp auth configuration

[Thomas Baudel]

In the following section:
https://help.ubuntu.com/11.10/serverguide/postfix.html#postfix-smtp-authentication

the proposed sasl security option, which will presumably be used by millions of installations, is as follows:

smtpd_sasl_security_options = noanonymous

I strongly recommend the following instead:

smtpd_sasl_security_options = noanonymous, noplaintext
smtpd_sasl_tls_security_options = noanonymous

 (see http://www.postfix.org/SASL_README.html#smtpd_sasl_security_options for description)

the reason: with the current proposition, postfix will authorize an authentication method that involves plain text passwords transmitted unencrypted over the network. This means a simple network snooper installed over a corporate network will be able to recover the passwords of users who use the ubuntu server as a mail relay.

conclusion: documentation should ensure 'noplaintext' is used by default for non encrypted routes.

[Bryce Harrington (bryce)]

Fixed for focal.

https://discourse.ubuntu.com/t/mail-postfix/11325