Ok, I’ve had an email server up for about a year, and occasionally we have emails we send detected as spam. I did have the reverse dns pointer records setup from our ISP, but I am questioning if I am using the correct settings. I am suspicious that these servers which are flagging our email as spam could possibly be set to perform reverse dns lookups, and seeing that the domain tied to our IP doesn’t match.

We have a domain, lets just call it mydomain.com
We have a static public IP address, and behind that address are several servers to handle our website, VPN, email, etc…
The A record for that domain points to our public IP address.

We have to MX records, the lowest number (highest priority) points to a hosted email filtering service which does offisite filtering and then delivers to our mail server. the 2nd MX record points to mail.mydomain.com.
There is also an A record for mail.mydomain.com which points to our public IP address.

the email addresses are in the format user@mydomain.com

I have the reverse DNS pointer setup to point to mail.mydomain.com
Should this have been setup to point to mydomain.com instead?
We are not open relay.
That was one of the first things I did when I setup exchange.