sendmail Deferred mail - reason unknown

["Sean Carolan" <scarolan@xxxxxxxxx>]

I'm a bit baffled by this problem.  Maybe there's a sendmail guru out there who can help me out here.  We have some end-users who need to receive system-generated mail that originates from a java-based application on our network.  The java app sends the mail through our sendmail cluster, which then sends the email on to the end-user over the Internet.  The size of the emails can range from a few kb up through around 2Mb in size.  

The mail logs show that these emails are typically delayed for up to 24 hours, sometimes longer.  It appears that several attempts to deliver the email are made, with each unsuccessful one showing "Deferred" status in the maillog.  After several hours of failed attempts the mail finally goes through successfully.  Here is a typical entry (customer name redacted):

exmx1 : Dec 14 05:28:39 exmx1 sendmail[31574]: mBDIYhEa031574: to=<customer@xxxxxxxxxxx>, delay=00:00:00, xde
lay=00:00:00, mailer=esmtp, pri=41874, relay=mail.example.com., dsn=4.0.0, stat=Deferred

Unfortunately there is no reason given for the "Deferred" status such as "Server unavailable", etc.  

Do you have any ideas how I can begin to troubleshoot this?
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