It is currently impossible to use an address containing a '+' character in the local part in the configuration panel.
This is quite annoying because I'd like the mails coming from DokuWiki to be sent to firstname.lastname@example.org
(I'm using Google Apps on my domain, and Gmail redirects user+something@domain to user@domain transparently and without any prior configuration).
Attached to this report is a patch that fixes that issue on my server. A better solution would be to use the EmailAddressValidator class, but I didn't try to do that as this one-liner is enough for me.