I actually host my own email. I developed an open source application for automatically encrypting all email with my public key as soon as it arrives, and I can't do this if somebody else hosts my email. You can read why and how here: https://grepular.com/Automatically_Encrypting_all_Incoming_E...
Brilliant! Thank you for sharing the post and code. I'd be interested in hearing thoughts on how to make it searchable. If you don't index, searching will take quite some time. I guess the best thing to do would be to index each e-mail (keywords?) before it is encrypted and then encrypt the index itself as well. There is a problem with the keyword approach though - if the index encrypts the words but the "link" between message id and encrypted keywords is not encrypted, then an attacker who is in posession of one or several other message bodies in plain text can see correlations between the content of known and unknown message bodies.
Did you try it and can compare it to gmail?
Especially on:
- linking other accounts (POP and IMAPS)
- spam detection