> Note that it's a pity to have to do all this computation when admin_email is defined.... I'd fallback only if admin_email is not defined.

You are right, , i will fix that.

>  why send the email with the admin email instead of the user's email?

 1 - Because all platforme use that 
      * Name of user <notifications@github.com>
      * Name of user <jira@xwiki.org>

 2 - This can blacklist the server and emails will be concédered as spam since  the domaine of the sender will be different from the server domaine. 

Our former Admin does not stopped to comment because of that, I personnaly have never been able to verify this information, But i found this is logic because it is not normal to send @gmail from our domaine instead of the gmail servur. 

For this reason i use the Admin email which will be carefully  added by the Admin (or the calculated email which use the same domaine as that the serveur)