OT: strange sendmail issue

[Chris Yuzik]

Hi everyone,

I'm having a rather strange sendmail issue. A couple of people cannot 
send email using our development server, while most other people can 
without problems. This seems to be more of an issue with their systems 
as opposed to their email client, but I'm not certain of this. We've 
tested on Outlook 2007, Vista Windows Mail, and Thunderbird. All have a 
different way of saying, "no such luck, buddy" (paraphrasing slightly) 
but more often something like "None of the authentication methods 
supported by this client are supported by your server" or similar.

When MOST people connect, after their mail client issues the "EHLO xxx", 
there is something that looks exactly like this:

    250-ENHANCEDSTATUSCODES
    250-PIPELINING
    250-8BITMIME
    250-SIZE
    250-DSN
    250-AUTH DIGEST-MD5 CRAM-MD5 LOGIN PLAIN
    250-STARTTLS
    250-DELIVERBY
    250 HELP


But when some users connect and after their machine issues the "EHLO 
xxx", they only get this:

    250 ENHANCEDSTATUSCODES


After which, their mail client promptly generates an error and it's all 
over.

We've confirmed the same behaviour from Telnet as well.

I thought it might have been related to unsigned-certificates on the 
server or something, but I don't think so.

Anyone have any ideas how to troubleshoot something like this?

Thanks,
Chris