Can connect to our mail server using telnet onto port 25 and this works correctly, 'ehlo whatever' shows output as expected.

However using a mail client to connect it gives an authentication error and the following appears in the maillog file;

did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA


Can you give me and tips on what to look for in the config, this works correctly on our development box but not on our production server. Could it be another program is interfering with the connection?

Sendmail is running in standalone mode not through the xinetd daemon.


Regards,


Edit:

Sorry I forgot to state I am using the PLAIN AUTH method as to try and avoid getting more errors.

Hi,

Have a look at this nice howto here at LQ.
Ditch the paragraphs regarding compilation of the needed software and pay attention in saslauth config and the sendmail server-side configuration
You might also use this to test your setup from CLI

Tip: In my case for this setup to work I had to use username@hostname (just the hostname not the fqdn) as the base64 encoded username.

Regards