PostGress is too much and SQLite3 might be to little. You might wanna check out other options. What is the problem with Maildir/ ? I/O heavy?? I don't think th

PostGress is too much and SQLite3 might be to little. You might wanna check out other options. What is the problem with Maildir/ ? I/O heavy?? I don't think that modern computers & filesystems will struggle with maildir. Please add GnuPG support. Also you could add mail folder encryption (e.g. having the emails encrypted in the system, key required to unencrypt them when mail client starts... key could be saved in the keychain for lazy users).