The regexp based email validation currently in place in DokuWiki fails on certain valid and invalid addresses. Most prominently IP based email addresses are not recognized as valid.
Currently 7 test cases fail.
It has to be decided what the goal of the email validation is:
a) being fully RFC conform
b) trying to limit registrations to sensible email addresses only
If b) is the goal we have to decide which of the currently failing addresses can be considered as not sensible.
A solution for a) would be to replace our regexp based approach with using a validation library like http://code.google.com/p/php-email-address-validation/