theres a open source isp tool, which probably is what you need.
Check: http://www.ispconfig.org/
But I think you will have to build your system from the ground, because this software only supports sendmail or postfix.
Another question is, why do you choose exim and want to use postfixadmin. I donĀ“t know this software, but I guess its for postfix :)
Another view of the problem is the following. These admininterfaces are in a certain way extremly specified. Not in the way you use them, but in the way how they need to be integrated in your enviroment.
There are so many different scenarios in how to setup a mail server and the administration, that these systems need a very very specific enviroment they fit in.
I would say it is nearly impossible to find a solution that fit your needs to 100%. The other way around, I bet also you don't find any commercial solution that fits 100% also. :)
I dont know exim, so I can hardly tell how you can get such a thing like user defined spam working, but I know postfix, and I would bet a great sum that you can customize Postfix to fit in your scenario. Personally I use sendmail and postfix and in the direct comparison postfix is much much more flexibel than sendmail can ever be (in its current version).
So to clarify this again, I have no idea about qmail and exim and maybe these two mailservers are extremly good smtp servers, but I guess they are not as flexible as postfix if you want specialized setups. And in most cases there are simple ways to go, to solve complex scenarios or needs.
Maybe I get some downvotes for this post, but I never had a problem which was not solvable by postfix. I mean, you can build regualr expression based hash maps, how cool is that :)
I wish you the best luck to find your solution, hope I could help a little bit to clarify things a bit and show you another point of view.
Best Answer
First, the word "pipelining" has two meanings in SMTP.
It sounds like they are speaking about #2. According to http://www.exim.org/exim-html-current/doc/html/spec_html/ch41.html#SECTmulmessam, with regards to pipelining to hosts over TLS connections:
What that means is instead of what you expect:
Exim does this:
The above is from memory, I can't recall if "end_session" included disconnecting or not. But I helped a guy troubleshoot this behavior once in IRC and he figured out that the above paragraph meant that it wouldn't pipeline in the first way described if STARTTLS was used to encrypt the session. So unfortunately, the only comment I have is that if you force no TLS for this particular host, it should start pipelining the way they want it, but I feel that is not a good answer at all as I believe all email transfers should be encrypted.