Will msmtp fallback to unencrypted connections if encrypted connections fail?

Question

My ~/.msmtprc config file says to connect to a server on port 25 with tls on and tls_starttls on. Is there a risk that, if the encrypted connection setup fails for some reason, then msmtp will fallback to a plaintext connection, possibly divulging the authentication passwords or email contents?

Answer 1

Warning: this is just my best guess, not a security guarantee. From a quick look at the msmtp.c file in the source https://git.marlam.de/gitweb/?p=msmtp.git;a=summary it looks like the msmtp_rmqs function and other relevant functions, in the case where HAVE_TLS is set and the account is configured to use TLS and STARTTLS, will indeed fail when there is an error setting up the encrypted connection, instead of retrying without encryption.