Gmail can be very strict with their email filtering when it comes to forwarded email, if you're testing the forwarder by sending from another Gmail address this is likely the cause of the email not forwarding on.
An address that is set to forward to mike@gmail.com, for example, will appear to not work if the email originates from mike@gmail.com as this will be filtered due to the spam-like characteristics of this configuration. Spammers will often send an email back to themselves whilst BCC'ing in the intended recipients, Gmail block such email meaning this will not get through once forwarded from our servers. If you are testing the forwarder by sending an email from the final destination address for the forwarder please test from another address to see if this is working as expected.
Whilst this is not always the case for other Gmail address (eg. mike@gmail.com eventually forwarding to morgan@gmail.com) this may be picked up due to the number of emails being forwarded through the servers and also be filtered. It's worth testing this from a non-Gmail account if this is your configuration for your testing and the emails aren't going through.
If this still fails when using a non-Gmail address please contact our support team through the ticketing system providing an example of the email that fails. Our support team will need the following information in order to investigate:
Email address this was sent from and to
Destination address of the forwarder
Time and date this was sent
