Recs.
Updated
SpecsUpdate
Pros
Pro Plug-in support
Roundcube allows third-party plugins and has a temporary plugin repository (until [the official plugin repository] (http://plugins.roundcube.net/) comes out of beta) with over a hundred plugins available, covering authentication, improved security and settings among many others categories.
Pro Sophisticated address book
Each contact can have their e-mail address, phone number, location, photos and associated URLs added to them. You can then group contacts and address your mails to the group instead of having to enter each person separately. Additionally, you can import vCards and CSV files as contact information. And, it has LDAP connectors.
Cons
Con Klu
Unfortunately, all interfaces of roundcube look very old. I hope there will be a progress soon, Google Mail and Outlook Webmail should be the role models here. But also Yahoo mail offers an intuitive design.
If this open source software should survive, it must be completely renewed and bring up to new standards.