> Since the original suggestion was to use IMAP to authenticate SMTP
> relaying, maybe you were thinking of the following method?
>
> You can use IMAP as a means to authenticate a user before he (or
> really, his/her IP address), is allowed to relay mail via SMTP. The
> idea is that users that have a valid IMAP account can be trusted, so
> you can allow them to relay mail as much as they like. In NetBSD
> pkgsrc you can find something called DRACD that dynamically adds
> IMAP-authenticated IP addresses to a database when a user logs in via
> IMAP. This database can then be used to allow relaying. I have used
> this with imap-uw and postfix for a long time and it works just fine.
>
> The advantage of this scheme is that it supports stupid Windows
> mailers that cannot do real authenticated SMTP.

could you point me to some URL about it?

especially dumb-guide for windows user how to configure outlook.