Re: Agree - fix the '+' problem first
> a) Accept it, but just strip it out so you don't actually get the emails
I registered on e-bay with an e-mail address that contains a | character in the local part. Everything works fine unless I try contacting support - then I get some bounces from their internal servers saying that | isn't a valid character (it is).
As for IDNs, I've had an IDN domain for a few years now, and I also have e-mail on it. The only users that have had problems replying to messages sent from this domain have been using gmail...