I think I've said good things about this project in the past. I'm doing it again.
Want your own web based mail client? rainloop rocks for a sane install process and just working well enough quickly. Needs php and php-curl and php-xml on a generic Apache/PHP server. Probably works the same with Nginx etc.
I mostly use it "disposable" or purpose limited email addresses and testing mail server stuff, but I'm considering using it more... Not sure of how well, but it claims GPG support. Hmm..