[jeroenhd]

So people with an exotic email address can't use your service because you don't think their email is valid? The reason you don't see those exotic addresses are mostly because of bad programs not knowing how email works.

This reminds me of that story of a Chinese man unable to get registered at the bank because the computer systems don't have a character required to write his name.

Sure, "it only affects a small amount of people", but it shouldn't be that hard to just flag strange but valid emails with "your email looks strange, check it again and tick this box if you're 100% sure you typed it right" instead of outright refusing to work. The check box doesn't even need to be interpreted server side, this can be done in one or two lines of javascript.