A simple idea and it helps bug wrangling greatly since you don't have to add '@gentoo.org' every time. This is probably something that should be fixed upstream. Implementation would encompass that the bug report/change forms automatically resolve any names added to Assignee/CC/etc. to @gentoo.org addresses or return a failure page. I remember requesting this a while ago, but maybe that was an informal poke in some IRC channel.
This should be fixed now through the bugzilla-4.x upgrade.
It's not. What bugzilla 4 does it to match it against every username / e-mail address in the database. That's good, but it isn't the same as applying the knowledge of domain names important to the project.
Which isn't to say I don't like that other feature, as it closely resembles what I was initially looking for. So feel free to close this bug report as WONTFIX or UPSTREAM (but not FIXED because it isn't).
WONTFIX it is (I like the existing functionality too, although it could be a bit quicker :/)
