Can't connect to windows box from Debian, can from Red Hat

[Marc Stein <mstein@egrad.com>]

This is a really bizarre situation.  I have not been able to send mail to a
specific Windows mail server at cw2.coreweb.com from a Postfix server on Debian.
 I cannot telnet to port 25 on the Windows machine from any Debian box that I
have.  I can telnet to the machine from Red Hat and Windows machines.  When I
send a telnet request from the Debian box I don't get a reply and the telnet
request times out.

What makes this particularly puzzling (to me, at least) is that the Debian, Red
Hat, and Windows boxes that I try to telnet from can all be in the same subnet
so it doesn't seem that it could be a firewall issue on the other end.

An example follows:

28206   2.279791 linux-dev.y2m.com -> 66.151.230.133 DNS Standard query AAAA
cw2.coreweb.com
28428   2.297725 linux-dev.y2m.com -> 66.151.230.133 DNS Standard query A
cw2.coreweb.com
28895   2.335775 66.151.230.133 -> linux-dev.y2m.com DNS Standard query response
PTR cw2.coreweb.com
28903   2.336422 linux-dev.y2m.com -> cw2.coreweb.com TCP 33038 > telnet [SYN,
ECN, CWR] Seq=3827497024 Ack=0 Win=5840 Len=0
66085   5.335152 linux-dev.y2m.com -> cw2.coreweb.com TCP 33038 > telnet [SYN,
ECN, CWR] Seq=3827497024 Ack=0 Win=5840 Len=0
140825  11.334452 linux-dev.y2m.com -> cw2.coreweb.com TCP 33038 > telnet [SYN,
ECN, CWR] Seq=3827497024 Ack=0 Win=5840 Len=0


Any suggestions, ideas, or comments like "Hey stupid, did you think to look
at..." would be greatly appreciated.