Is your GAFE e-mail domain the same as the Moodle domain, and using the php mailer in Moodle?
If so, it simply means the server can't tell the difference between itself and forwarding to GAFE. You'd need to use the GAFE test alias as the forwarding address instead so the server knows it's actually somewhere else.
I had (well, technically still have) the same issue but we don't create student e-mail accounts; it only occurs with faculty e-mail. I have two domains though and a legacy one is the default one-it might break some calendar ownership things (according to Google) if we switch it. But this would allow me to use the test-alias on our domain for GAFE e-mail forwarding.
If it's not this, please ignore . I'm not too knowledgable on e-mail but I am familiar with the issue described above insofar as it relates to using the same domain for both.