Email/MMDF delivery failures - help needed

[System Operator]

I am running SCO UNIX Sys V 3.2.  I have an email problem.
Email from other machines does not always get delivered.
It usually does, but not always.  Sometimes it gets delivered
with a garbled header.  

When these problems occur, a copy of the letter can usually
be found in /usr/spool/mmdf/lock/home/msg, with an ungarbled
header.  I have not found a reference to this directory in the
docs yet (though I confess I have not read every word of every
manual since I need a solution within my lifetime), and have
no idea what it means.

Can someone suggest ideas why email from certain machines sometimes
gets delivered and other times is dumped into the directory
mentioned above?  The email has a correct address (user name).
The machine has plenty of disk space.

Dean
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