Hi,
I can’t signup with an .io email address, the email is invalid…
That’s not a very descriptive post, and is also out of context for these forums. To report a Twitch bug, use the bug reporting tool: http://www.twitch.tv/bug_reports/new
For what it’s worth, I was able to register on the Twitch site using a test “.io” domain extension just fine. It’s possible you mistyped something.