There are too many webmail clients are available on web.
Choosing best out of them is quit difficult task for any one.
After exploring tens of webmail clients, I will vote for following webmail client as top 3 webmail clients:
- Roundcube: I would rate it as the best and easy to install. It has rich text editor and clent side filtering support. Also it hase good web interface.
- Zimbra: Not explored much about, but based on futures its quite a popular webmail
- SquirrelMail: Its basic webmail with basic web interface. There is no rich text editor support. There are lot of plugins available for SquirrelMail.
- RainLoop: Recently I seen this webmail client so thought to share. UI is good in RailLoop. I am not tested it but when I walk through installation procedure its looking straight forward and easy.
All above webmails are open source.