Re: Back to Reverse DNS

[Scott Klement <midrange-l@xxxxxxxxxxxxxxxx>]

> And as long as we are on that does anyone have a good link to how that
> works. I tried it once and it did not work (I have control over the mail
> server so I know it will handle it) but from the client how does the
> communication have to work (start on port 110 but how do you switch to
> port 25).


You don't start on port 110 and then switch to port 25.  They're two
separate things.  First you use POP to get your mail.  Then, you use SMTP
to send your mail.

You see, there's no official authentication involved in SMTP, but POP3 has
a username and password associated with it.  So, when you log in with POP,
it maks your IP address as "trusted" so that SMTP will relay whatever it
is that you have to send.

This is really intended for dial-up users.  They dial-in, then open up
their mail client -- what's the first thing the mail client does?  It
checks the server to see if there's any mail -- in other words, it logs in
with POP3.  Then, when the user is ready to write mail, he's already
authenticated.

The only tricky part is that the IP address "times-out" and doesn't remain
trusted -- this is necessary, since the SMTP happens entirely after the
POP3 is done, there's no way to tell when the user is done -- so it times
out to prevent that IP address from simply being good "forever."   The
reason why this causes problems is that people will sign on, check their
mail, then read their mail -- possibly for a long time -- before sending
anything.  If the address has timed out, the send will fail -- but it's
easy enough to fix, they just have to check for new messages again.

For an iSeries environment, however, I'm not sure that POP before SMTP
makes much sense.  You could write a quick program that connects and sends
the userid and password to the POP server (20 minute job for me) and then
it would send the mail -- the problem is, how do you know when to run the
POP program?

If the IP address times out after 20 minutes, you could keep running the
program every 20 minutes, I suppose.

Or, you could get a static IP and an ISP that's willing to permanently
trust that IP address -- that way you don't have to mess with POP before
SMTP.

Does that help?  Or are you asking something else completely?