Yup, the problem with well-known ports is that well-known port numbers
get either (a) blocked by misguded ISP's, or (b) transparently proxed
by misguided ISP's. Since I have no idea what sort of stupidity I
might encounter at various different hotel, conference, or 802.11
hotspot networks, it's more convenient for me to use a non-standard
port.
Another approach is to tunnel your SMTP connections over
SSH. So far most ISPs that block port 25 do seem to permit SSH.
I've been saying for some time that the single most important role for
encryption on the Internet may well be the defense of its end-to-end
model against encroachment by greedy, incompetent or misguided ISPs.
The MUA issue isn't important in my case, because I run a local MTA on
my latop (exim), which is configured to do the STARTTLS and AUTH, so I
can use any MUA I wish.
Ah, but then you're running a *mail server*, which puts you in
violation of your local ISP's rules even if your MTA does not permit
relaying!
Believe it or not, I have actually been given this exact argument by
someone at MAPS whom I've been trying (unsuccessfully) to convince
that the MAPS DUL is a fundamantally flawed idea.
This is the mentality we're up against. I think a clear statement
by the IAB/IETF, even though it would not be binding in any legal sense,
would carry a lot of weight against this kind of braindamage.
Phil