mail-crypt implementation

[snoopotic]

Recently, by default, all E-Mails (using postfix/dovecot) are stored unencrypted. So if someone has access to the mail directory/filesystem backend, they could read the e-mails.

As solution, I‘d like to suggest to use the mail-crypt plugin:
https://doc.dovecot.org/main/core/plugins/mail_crypt.html

This could be made configurable and also global or user based encryption would work. I‘d personally suggest to use the directory/user based one and use the user password for the key unlock-password as well.

It would need an implementation to change the key as well when the user changes his password. It would also possibly need an initial key in read-only-mode if something got wrong to be able to read older e-mails. (We may need to think/discuss about that more if the idea/request is accepted.)

[d00p]

Using per-folder keys is not considered production quality, but global keys are fine.

Mail crypt plugin can operate using either global keys or folder keys. Using both is not supported.

Basically a good idea, but tbh a lot of work, this might be something for froxlor-3.0 (dont want to start such a big thing on 2.x now with 3.0 already in planning/coding)