> I discovered the problem... v4.51 doesn't accept my existing UDG settings.
> 
> I had the file format setup as "~(username)~(random).101" but after I changed it to "~(random)~(random).101" the M/32 gateway works fine.
Strange, I thought the root name was always limited to 8 characters maximum even in v4.41 and earlier, I have no idea how that worked.  By default this is the set to create a 8 character root using the  ~d~d.101, I have no idea how ~8~d.101 would work in creating a lot of messages in the queue.
   ~c       The full path to the file containing the message
   ~t       The address to which to send this message
            (note: this is not necessarily the To: field)
   ~s       The message's subject field
   ~f       The full form of the message's "from" field
   ~n       The sender's user name in its simplest form
   ~b       The sender's bindery id, as a long hex integer
   ~8       The first 8 chars in the sender's username
   ~y       The time and date in RFC-822 format
   ~d       A random integer, expressed as 4 hex digits
   ~q       Y if this message is a BCC, N otherwise
   ~%name%  The value of the environment variable %name%.
   ~p       The user's personal name preference
   ~x       The name.ext ONLY of the container file (no path)
   ~a       The directory from which PMail was run (or base directory)
   ~h       The current user's home mailbox location
   ~w       The current user's new mail location
   ~~       A single tilde character.