Auth error when sending mail through Postfix with SSMTP

I'm trying to send mail from server A running SSMTP via a server B running Postfix. The Postfix server is running just fine and has been in production for a while without any problems. It runs Postfix with Dovecot. I can use my Gmail account to send mail from SSMTP and that works however I want to use my own Postfix server because I want more control over the entire mail process. **In the next logs and code I have replaced my own public domain with example.com.** Here is the error that SSMTP produces: root@N40L:/etc/ssmtp# echo "test" | mailx -vvv -s "test" martin@example.com [] EHLO example.com [] AUTH LOGIN [, method=PLAIN, rip=::1, lip=::1, mpid=14050, secured, session= Jan 16 10:46:12 dovecot: imap: Debug: Loading modules from directory: /usr/lib/dovecot/modules Jan 16 10:46:12 dovecot: imap: Debug: Module loaded: /usr/lib/dovecot/modules/lib10_quota_plugin.so Jan 16 10:46:12 dovecot: imap: Debug: Module loaded: /usr/lib/dovecot/modules/lib11_imap_quota_plugin.so Jan 16 10:46:12 dovecot: imap: Debug: Added userdb setting: plugin/email=n40l@example.com Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Effective uid=5000, gid=5000, home=/var/mail/vmail/example.com/n40l Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Quota root: name=User quota backend=maildir args= Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Quota rule: root=User quota mailbox=* bytes=10737418240 messages=0 Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Quota rule: root=User quota mailbox=Trash bytes=+104857600 messages=0 Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Quota grace: root=User quota bytes=536870912 (5%) Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Namespace inbox: type=private, prefix=, sep=, inbox=yes, hidden=no, list=yes, subscriptions=yes location=maildir:/var/mail/vmail/example.com/n40l Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: maildir++: root=/var/mail/vmail/example.com/n40l, index=, indexpvt=, control=, inbox=/var/mail/vmail/example.com/n40l, alt= Jan 16 10:46:12 dovecot: imap(n40l@example.com): Disconnected: Logged out in=50 out=475 I can log into server B's webmail without any trouble and send and receive mail for the address I'm using so the account itself is in order. I tried other accounts and they produce the same errors. I'm at a loss. SSMTP should be able to send mail through Postfix. Even with all debug and verbosity options on, I can't find the source of the problem. Any help is greatly appreciated.