Re: [Exim] RBL DUL and SMTP AUTH

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Author: Peter Radcliffe
Date:  
To: Exim Users
Subject: Re: [Exim] RBL DUL and SMTP AUTH
"Michael J. Tubby B.Sc. G8TIC" <mike.tubby@???> probably said:
> This has caught me out too, and turns out to be a right problem :-(
>
> When working overseas using a local ISP for access to the net (dialup)
> I can get my email from my IMAP server but cant send out via our
> mail relay because while I have enabled SMTP Auth and setup some
> usernames/passwords it also has DUL/RBL enabled for SPAM prevention.


The only real way to work around this is to set up a different mail
server (I have another copy of exim listening on a high port) that
will only relay (or do anything else) with SMTP auth and does not do
RBL type checking (since the only thing it can accept is authed mail
it doesn't need to). If you are not already, TLS is a good thing to
set up at this point, too.

If your clients can change the port number they send to it can be on
the same IP, same machine. The advantage of changing the port number
is then you don't fall foul of remote ISPs that
filter/block/devnull/transparent-proxy port 25. Mail sent directly out
from port 25 on some ISPs networks will silently get dropped on the
floor. Attempting to send AUTH mail through a server that does not
handle AUTH can let your password get seen/stolen in cleartext.

I roam with my laptop which runs FreeBSD. exim on my laptop is set to
smarthost to my mail server on a high port using TLS and AUTH and
failing if TLS is not supported. Before I started using the high port
I found all sorts of weird and not-wonderful port 25 systems :/

> > In Exim 4, all the checking happens at the time of the RCPT command,
> > and so what you want to do will be possible. However, it will be many
> > months before Exim 4 is released (and some more before it is stable :-).
> Intersting to note, but I could still do with a fix now...


I worked around the problem quite happily.

P.

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