I got a recommendation for a mail plugin from Binkydude. I had a mail plugin before but we disabled it since it allowed only one-liners and I started to get half-written mail from every second user on the server. This one here however allows to write longer emails. And they are even delivered by a Villager!
Check out the plugin page for a manual. I will put up a page later. Please make sure you do not spam people, otherwise I have to block you from sending! So please try it out and tell me if it works!