Datagram forwarding for email with attachments

[Neil Palmer <NeilP@xxxxxxxxxxx>]

A customer system (small model 150, V4R5 with latest PTF cum pkg) is set
up for a TVP/IP dial-up Internet connection to their ISP.
Datagram forwarding is turned on in CHGTCPA.
PC's run Outlook or Netscape mail to an ISP on the Internet (using email
addresses supplied by the ISP), and the 400 forwards the data from the
local LAN out via the dial-up ISP connection with no problem - UNLESS
there are attachments to the email being sent.  In this case the dial-up
ISP connection seems to lock and you have to force it down and restart it
again.  Next time someone tries to send an attachment, same thing.
If they connect the individual PC's running email directly to the ISP via
dial-up, the mail with attachments works fine.
Anoyone else experience a similar problem ?

...Neil