Issue Auto Forward emails are bounced back

[jj66]

Forwarding is enabled to auto forward to a @Gmail address.

@domain -> @Gmail

When I send to @domain, I receive a bounce back email:

Message Delivery Failure

MailEnable: Message could not be delivered to some recipients.

The following recipient(s) could not be reached:

        Recipient: [SMTP:mad:gmail.com]

        Reason: 550-5.7.1 [x    12] Our system has detected that this message is

I tried sending from @domain from webmail and @Gmail receives the email successfully.
It seems that gmail only rejects the email from @domain if it was sent through the Forwarding feature.