Incoming mail(verified by support) has a bug that when email is sent from an entity like mike@att.com and is signed by att.com, and we receive it at dean@mydomain.com, when the route gets applied, it also incorrectly swaps out the att.com with mydomain.com security key invalidating the email security. Gmail then throws this email in the spam folder.

outbound email works fine since it comes with a FROM address of mydomain.com and so when mailgun swaps in a signedby, it is 100% correct since it is the MX record for mydomain.com and the security is all setup.