My company currently uses SquirrelMail for webmail access. Our creative/graphics division wants to customize the look/feel of the interface to match our coporate branding, etc. The work they want to do goes far beyond what SquirrelMail templates/stylesheets can accomplish. They are looking more along the lines of www.voxthemes.com or www.nutsmail.com.
After doing some research, it doesn't seem like SQM can be easily customized as heavily as we want. For example, the sites mentioned above release cusomt version of SQM sources. So I'm looking for some alternatives to SQM. I've been reading these forums/google a lot and it seems like there are a few big players here:
IMP/Horde (www.horde.org) -- Haven't done too much reading on customization, but it looks like a popular alternative. Well supported and maintained.
RoundCube (www.roundcube.net) -- Looks promising, but young (barely 6 months old). Security is a concern, and young apps don't give me a lot of confidence.
OpenWebmail (www.openwebmail.org) -- Its out there, but doesn't look very promising.
Does anyone have any experience with any of these apps? Particularly w/ creating custom user interfaces? Advise is appreciated.