Many thanks to Rick Warner, Adam Shostack, Russ Cooper, Todd Truitt, Mathew
Patton, Michael Dillon for replying, all with very helpful information and
suggestions. I may yet summarize to the list, except I see most have already
copied this list so there is not much point in repeating everything. I thought
this from Todd Truitt was very interesting:
Todd> DOS is single threaded and multiple SMTP connections will fail.
Adam Shostock fascinated me by the suggestion the DOS box could be overtaken if
its possible to buffer-overrun the SMTP app running on it.
Rick Warner wrote interestingly about Charon likely being the app. At this
stage, I do not know if they wrote the SMTP app, but one thing Rick maybe
missed was that there IS an IP network on the inside. My understanding is:
Internet and IP --- DOS 5 SMPT app --- IPX only --- SMTP hub --- IP internal
We don't know what or how smart the SMTP hub is but we do know there is one of
about every OS you can think of on the inside IP network.
Others pointed out the real risks are elsewhere, inside. True, except I should
have mentioned they have small network of sacrificial hosts with Internet
access which is always available to any user at any time for any purpose and
they are quite comfortable with the outcome too. But the purpose of my
original post was to focus everyone's attention on the DOS 5/SMTP "firewall".
Thanks to all who replied.
John L Hardcastle, Director, HARDCASTLE ELECTRONICS LIMITED
P O Box 74028 Market Rd, Auckland 5
Level 7, Eden House, 44 Khyber Pass Rd, Grafton, Auckland, NEW ZEALAND
Tel +64.9.366.1502 Fax +64.9.366.1554
Internet: john @