Qmail SMTP works... sometimes... other times it times out.

[cult hero]

I've got Qmail/vpopmail/courier running on two servers and I've never bothered with SMTP for remote users before because we've always just used our ISP's. However, I have a funny situation where a friend will be at a hotel using their connection which, because it's for temporary purposes, doesn't have an SMTP server.

As such I wanted to set it up on my servers. THe ultimate result I get is strange.

From any machine on my cable modem (I've tried at three locations and all are behind NAT) I get a timeout trying to telnet into port 25. However, when I ssh into a foreign computer they connect just fine.

Any ideas as to what could be causing my connections to time out? Could it be the router? Is there something my ISP might be doing? Or does it sound like a server configuration issue? If you have any specific questions I'll provide the info but I'm guessing if anyone is going to answer this, they had the same problem before.
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Repeat after me! This world is made of love and peace!

[DaveArb]

Your ISP may be blocking port 25 entering/leaving their network. This is becoming more common due to large numbers of direct-to-MX spam trojans.

Dave