Current Situation
One defined email address has to be configured as "From Address" when sending email notifications (on Admin Console -> Mailserver). All notification emails are sent from this address. When recipient "blindly" replies to this email, it is sent to the defined address rather than to the modifier causing the notfication to be sent.

Desired Situation
On general Mailserver configuration, the variable ${email} is available for "From Address", just as it is available for "From Name":
http://confluence.atlassian.com/display/DOC/Configuring+a+Server+for+Outgoing+Mail
Meaning: Emails should be sent from the address of the modifier. In this case, the recpient will directly contact the modifier when replying to the notification email.