Far from complete, but some notes on the few I tried. First, this is for a setup basically following this linode guide for postfix, dovecot and system user accounts. I’ve slightly modified it to work with multiple domains. 
I have a few requirements, first and foremost that it must be able to support multiple sender identities. This will be used by people who have mail from multiple accounts collected here, and they need to be able to reply as that account. Secondly, the address book must be able to support groups. My mother users the webmail while travelling, and she has come to depend on this. Thirdly, and not _quite_ as essential, it would be nice to be able to filter messages into a different folder. (I know that this could/should be done server side, but my mother wants to be able to do this herself, and a) she’s not going to configure postfix, and b) I’m not always going to be around to configure it and c) I don’t even (yet) know how to do that)
Imp – discarded due to excessive requirements. I’m not looking for groupware
Squirrelmail – near effortless install.
apt-get install squirrelmail I then had to add an Alias/Directory config somewhere in apache. Squirrel provides the basic config in /etc/squirrelmail/apache.conf. I added this to my apache config, and presto, it all worked. Multiple identies works easily, but address groups comes via a poorly packaged and documented plugin, which I didn’t even bother trying out.
Atmail open / @Mail Open source – nice slick installer. Then pretty much epic fail. It is incompatible with dovecot out of the box. It tries to login with a full user@domain, which doesn’t work when I’m using system accounts. There’s a fairly well known hack to make it work, but this didn’t inspire confidence. Address groups worked out of the box, but you only get a single identity. (With the login hack, you can actually logout and back in again to get a new idenity, but that is just worthless)
Roundcube – I left this for last, as I’d heard it was notorious for being bloated, sluggish and full of security holes. It may have security holes, but most stuff does, and it’s certainly not bloated and sluggish anymore. I’m using version 0.5.1, and it is so far much much better than the rest, and the only one I’m going to be opening up for my mother to try out. Installation was not quite effortless, but pretty good. The installation instructions for setting up the db ahead of time are pretty good.  A slightly unusual copy/paste from the generated setup webpage to the config files on disk, but hey, it works pretty well.
Multiple identities work, and are intuitive to both setup and use. Address groups work, but are not quite as easy to use. The setup wasn’t instantly obvious (There’s a plus button on the bottom of the screen) and adding users to groups wasn’t immediately obvious either. You just drag them over the group name. :) I guess I’m used to older webmail clients :) Also, to send mail to a group, you need to start typing the name of the group in the To: field. I haven’t found a way to select a group/groups from a checkbox.
I ignored BlueMamba and IlohaMail for having no recent updates. I’d had quite enough of trialling webmail by now, and roundcube was clearly in front. I’d be interested in hearing any other suggestions though if anyone’s out there :)
- I had to add a
virtual_alias_domains = ekta.isfor each extra domain, and I had to add the base domain to the
mydestinationline in postfix’s main.cf file
- roundcube supports a few different databases, including sqlite, but only sqlite2 ?! what decade is this?