Having trouble sending to Gmail? (resolved)
If you’ve had trouble sending to Gmail addresses today or yesterday (December 14 or 15), where an address that you know is valid bounces back with “The email account that you tried to reach does not exist”, the problem isn’t you, or us. Gmail had a problem that caused this for all senders, seen on their status pages yesterday and today, with the latter confirming “Affected users received a bounce notification with the error “The email account that you tried to reach does not exist” after sending an email to addresses ending in @gmail.com”.
They also confirmed it on Twitter:
They say the problem is resolved now, so if it happened to you, it should work if you try sending again.