I haven't found out yet for this one; I'm just trying to find out where I'd
change it on if that were the case.
I don't think you can change it. I was thinking about describing how you
could work around this, then thought to myself "does it make sense to go
through all that trouble, if the managed mail server can't handle it
anyway?"
I dealt with a similar problem a few years ago.
I wasn't using a managed mail provider, however. I had my own SMTP server
(a FreeBSD machine) out on the Internet that I had set up, and could
reconfigure as needed.
My ISP blocked port 25. I switched to using 2525, and that worked for a
month or so, then the ISP blocked that as well. So then I used 8025, and
again, it worked for a month or so, then they blocked it.
I then set up a Sendmail SMTP server on a FreeBSD box on my LAN, and
configured a customer "mailer" in Sendmail that called a script on the
machine. The script opened up an SSH channel between my LAN's FreeBSD box
and the one out on the Internet that I used for SMTP. It sent the message,
and on the Internet side, it redirected the mail to port 25, and sent it.
Then, the machines on the LAN (including the iSeries) just forwarded their
mail to the FreeBSD machine.
The problem was solved because the data was encrypted and sent over SSH.
The ISP didn't know that the data was e-mail, and even if they did, they
couldn't very well block SSH without aggravating a large number of their
customers.
The big difference, though, was I had control over both ends of the
connection, whereas you would have to get cooperation for your managed
mail provider to do something like this.
