I've been running sSMTP as my mailer daemon for a long time using my google apps domain as mail server.
The config for this was pretty simple - /etc/ssmtp/ssmtp.conf:
email@example.com mailhub=smtp.gmail.com:587 rewriteDomain=domain.tld hostname=server.domain.tld FromLineOverride=YES AuthUserfirstname.lastname@example.org AuthPass=users-gmail-password AuthMethod=LOGIN UseTLS=YES UseSTARTTLS=YES
This has been working fine.
Recently I noticed mail was not getting through. I now see in the logs:
Creating SSL connection to host SSL connection using RSA_ARCFOUR_SHA1 Authorization failed (535 5.7.8 http://support.google.com/mail/bin/answer.py?answer=14257 <mail.id> - gsmtp)
I've checked the password. I can log in to the web with it and send mail via the gmail web gui just fine.
I've turned on two-factor auth and set up an app specific password.
I've checked that SPF and DKIM are set up on the domain (a bit cargo-culting here - found this on a google help page)
Nothing helps. As far as I can see - everything is correct just that google will no longer accept mail from this ssmtp instance - and I have no idea why :(