Gmail does not allow looping fowarders. If you've set up an email forwarder to a Gmail account and are sending messages to the forwarder from the same Gmail account, the message will not arrive. The forwarder should work perfectly for all other emails. This is a known attribute of Gmail accounts but this also may be the case with other email service providers, so if you run into any issues when testing a forwarder you've set up, you should first try testing the forwarder from an email address that is not the forwarder's destination address.