I'm running a piece of software on a Windows server that sends email notifications via a remote SMTP server. It has very few configuration options, and only supports basic SMTP authentication without SSL/TLS. I have exim4 running on a Debian server that will be the SMTP server for this Windows program. It is set up with default configuration, plus allowing AUTH PLAIN and AUTH LOGIN unencrypted connections. I have successfully sent an email over telnet:
telnet servername 25 ehlo test 250-AUTH PLAIN LOGIN ... auth plain XXX 235 Authentication succeeded mail from: ... ...
However, the program I want to connect to this server fails to connect. To see why, I ran a packet sniffer during the connection, and see the following session:
C: HELO hostname S: 250 Hello hostname C: AUTH LOGIN XXX | XXX S: 503 AUTH command used when not advertised | 500 unrecognized command C: QUIT S: 221 closing connection
I'm not familiar enough with the SMTP protocol to understand what's going on here. What do I need to change on my exim4 SMTP server to allow for this connection to be made?