* develop-olympus:
[ticket/10158] Remove some code duplication from generating the message.
[ticket/10195] Return false in session::check_dnsbl() when IPv6 is passed.
[ticket/10158] Only view "Return to" links if they are useful.
[ticket/10158] Add return-link to folder, when the user replied from a folder.
[ticket/10158] Add "Return to Inbox"-link to "PM send"-message.