itch.io

I do not understand what that means. There is no "a gmail". There is email and there is service providers. Your service provider seems to be gmail, but it will still send an email. If that bounces, it could be temporary server problems or some obscure reason like the one I linked.

Whatever the issue is, this message board is not the Itch support. There is no support team reading here. It is users answering here.