Why doesn't forwarding to Gmail work when I test it?
If you set up a forwarding e-mail address that delivers messages to Gmail, then test the forwarding by sending a message from that same Gmail account, the test won’t work. We’ll forward it properly, but Gmail won’t put the forwarded message into your Gmail “In box”.
(A similar problem happens with mailing lists.)
Can you give me an example?
Let’s say you set up “forwarding@example.com” to forward e-mail to “example@gmail.com”.
If you send a test message from “example@gmail.com” to “forwarding@example.com”, the message will be forwarded by our servers, but Gmail will discard the message.
This problem makes it look like the forwarding doesn’t work, even though mail sent from any other address to “forwarding@example.com” would work properly.
If you want to test an address that forwards mail to a Gmail address, send the test message from any address except the final Gmail destination address.
Why does this problem happen?
Gmail does this intentionally. According to their help page:
Mail you send to an account that forwards messages to your Gmail account will only appear in “Sent Mail”. This is intended to prevent clutter in your Inbox.
We think this is a misguided policy (it causes a great deal of confusion), but it’s something they control, not us. It happens with any mail forwarded to Gmail, not just mail forwarded by our company.
(Google has removed their original help page that described this for some reason, but it's still visible at The WayBack Machine.)