I need to set up a mail server on an Ubuntu Linux box. Instead of starting from scratch I'm looking for an all in one package, like a bundle that offers a complete but minimal and light weight solution.
I'd like this bundle to have at least the following characteristics; based around Postfix, some form of spam handling and a web interface the manage accounts etc.
"Complete but minimal and light weight solution". Uhm...
Just build it yourself. It'll be a lot more flexible, and you'll have a better chance of fixing it when it breaks. The components I'd use are:
I've had good luck with Zimbra at a previous company. The web interface is nice and all the components are self-contained, and the support forums are wonderful. It is basically all the popular open source mail tools bundled together with a slick interface.
However, these days I would (and do) outsource my mail handling to Google Apps for my domain.
Don't forget about Exim. Its a pretty straight forward, clearly documented (make that excellent documentation) and well supported by it's community. I have used Qmail, Postfix, and Exim. Exim without a doubt has served me best.
Of course the whole thing is subjective and any of the mentioned applications would work just as good as any other.
Second the recommendation to outsource. Yes, you could set up and run a mailserver yourself, but that means you're the one getting the page at oh-dark-thirty when something breaks. I like Fastmail, but there are plenty of other companies out there (e.g. Google).
If you need to run this system in-house for some reason, Zimbra meets your requirements and my employer's instance (supported by a 24-hour NOC) works fairly well.
You're going to have to do some setup of several components, that's the linux way - take a MTA, a spam tool, a web server etc etc.
However, your request is one that many people already want, so the steps to put them all together are well documented.
Try this one for example (plenty of other good setups in that site too)
For a web interface to practically everything, make sure you look at Webmin. It is the essential admin tool I use, next to ssh!
there are a few that have a lot of features all-in-one, but I think you'll still need to set up the MTA separately. For example, there's Horde or Zimba which appear to be good groupware servers.