Change mail-to alwaysdata redirection when reply to a notif by mail

What needs to be done

-Today when we receive notif by mail and we want to reply by email, this is the server that is in reply. We would like to redirect this mail-to, to the local admin (comu sitter) if needed. Not too sure if it's clear.

Also where can we edit some parts of this kind of message ? We should do something smoother in UX

Technical details

Are there any technical details worth mentioning?

Test cases

Describe here the tests needed in order to validate this feature

1. Step 1 open a notification by email
2. Step 2 click reply
3. Step 3 see that reply goes to server alwaysdata.net

Links & Mockups

1. Link to user story in wiki

2. other related Gitlab issues