[HanoiLUG] Introductions...and a question

[Steve]

Hi to ye all!

Name is Steve (from Cape Town) and worked in the security field for many years.
Current interest is Elliptical Curve Cryptography (encryption etc is
what I enjoy most)

Other than that I lecture Math/Physics at university.

Ok enough of the jabber...

I need to implement a better spam blocking solution than simply
filtering and RBL, so I believe greylisting will do the trick.  However,
there may still be false positives, especially if spammers use real mail
servers to do their dirty work instead of simple PC based SMTP engines.
So what I would like is a facility whereby the first time that an email
is sent to a user, the sender gets a mail back requesting positive
confirmation, like for example entering the text from a graphic (like is
commonly used on web signup services.

sqlgrey will do the basic greylisting, but does anybody know of software
that will do the rest?  Commercial OSS is fine as well, it doesn't have
to be gratis.

I've considered using a complete solution like scalix, but I don't think
that will address the issues as well as if I integrate specific modules
into a postfix (or exim?) server.  BTW what are the advantages of using
exim over postfix?  Postfix seem ubiquous and there are a gazillion
plugins and extras available, so I'd really like to hear what other have
experienced in this regards.

All your comments on this are much anticipated and appreciated