NAME
       DeleteUMSMsg -- Delete a message.

   SYNOPSIS
       success = DeleteUMSMsg( login, msgNum )
         D0                     D2      D3

       BOOL DeleteUMSMsg( LONG, LONG);

   FUNCTION
         This  functions deletes a message, specified by number, from the
       UMS MB.
         It does not necessarily free space on the hd, but it removes the
       message  logically from the MB so that no other user can access it
       anymore and it won't affect the dupe-check for new messages.
         The  MBP  may need reorganization to physically remove logically
       deleted messages.

   INPUTS
       msgNum  -  Number  of  the  message to be deleted.  As returned by
                   UMSSearch() or  WriteUMSMsg().

   RESULT
       success  -  Inidcates  whether the message was actually deleted or
                   not.   It  will  be  not  deleted  if  you  don't have
                   write-access  to  this  message or the message doesn't
                   exist.

   NOTES
         The  number of a message is valid only as long as you are logged
       in.  After  UMSLogout() messages numbers may change!
         So  you  always  have  to  use the real Message-ID to remember a
       message persistently.