sendmail Broken Pipe Error

Dear FreeBSD friends,

Lately I have setup a new FreeBSD server with 10.0-STABLE. Most of it went
smoothly. However I have an issue with sendmail. Some of the mails can be
sent out correctly, some of them stay in /var/spool/mqueue/. The provided
error messages are in the latter case:

Mar 24 14:16:01 MyServer sm-mta[11725]: s2ODCWT4011717: SYSERR(root): timeout writing message to MyProvider.com: Broken pipe
Mar 24 14:16:01 MyServer sm-mta[11725]: s2ODCWT4011717: to=<SomeAddress_at_example.com>, delay=00:03:29, xdelay=00:03:26, mailer=relay, pri=1284849, relay=MyProvider.com [XXX.XXX.XXX.XXX], dsn=4.0.0, stat=Deferred

I'm using Version 8.14.7
All was fine when I was using Version 8.14.5.

Since there is a timeout error, I like to know what sendmail is writing to
MyProvider.com

Is there a way to debug sendmail to disclose the message written to
MyProvider.com and the response from MyProvider.com. I'm pretty sure that 
there lays the solution to my problem.

Any help is highly appreciated.

-- 
Met vriendelijke groeten,
With kind regards,
Mit freundlichen Gruessen,
De jrus wah,

Wiel

*************************************
 W.K. Offermans