"plain" login authentication not working in Server 4
In /Library/Server/Mail/Config/postfix/main.cf, I have the line:
smtpd_pw_server_security_options = cram-md5,login,plain
In /Library/Server/Mail/Config/dovecot/conf.d/10-auth.conf, I have the line:
auth_mechanisms = cram-md5 apop plain login
But plain logins aren't working, even SSL-encrypted. CRAM-MD5 is the only thing working for IMAP, SMTP-AUTH, etc. Even local connections from mailman are broken, because the SMTP-AUTH module for 2.x only uses plain.
This was all working perfectly under Mavericks/Server 3, but apparently something changed with Yosemite/Server 4. Any ideas?