Remote User's SMTP relay authorization

[Andrew J Caird]

Quoting John Gibson <gib at edgate.com>:

> Roaming ( my def.) : Users who access the internet from multiple IP 
> addresses most of which are dynamically allocated (therefore unknown in 
> advance).
> 
> We do not want to support  permanent email storage at this time.  We 
> just want people to be able to retrieve their mail and provide SMTP 
> sending capability.  We want the IMAP/POP mail server to not require our 
> linux host to have system logins for any of the mail users.  We want a 
> scalable solution which can be flexible when our requirements change. 
>  We would prefer to allow users to select their own mail client (or at 
> least provide a list of ones that will work with our setup).
> 
> The SMTP sending capability seems to be the biggest issue.
> 
> Any suggestions would be much appreciated.

There are two popular ways of doing this.  The first, and preferred by most, is
SMTP AUTH - I believe that support of relaying for roaming, authorized users is
one of the reasons SMTP AUTH exists.  This, however, isn't a Cyrus question,
but an MTA question, and is better researched where ever you find information
about your MTA of choice.  The second is POP-before-SMTP, which is, in general,
a bad hack, but might be worth investigating.  Essentially, there is a third
process (not the POP3d or SMTPd) that looks at the POP logs and tells the SMTPd
that it can allow sending from IP addresses that had recent successful POP
sessions.  This involves a tight integration between your POP server (one of
many) and your SMTP server (again, one of many).  Because of the large number
of possible combinations, this is generally not well supported, but Googling
for "pop before send <my MTA name> <my POP server name>" might turn up
something for you.

Hope this helps, good luck (and, imo, you should use SMTP AUTH+TLS, with SASL
passwords).
--
Andrew Caird
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