MX and PTR on different outgoing IP

Hi all,
I`m looking for solution how to set revers dns for my mail servers

i have this situation
mx mydomain.com:
smtp1.mydomain.com > 1.1.1.1
smtp2.mydomain.com > 1.1.1.2
smtp3.mydomain.com > 1.1.1.3
smtp4.mydomain.com > 1.1.1.4

but all traffic that goes from these servers are going from address 2.2.2.2 (just a gaveway and nothing is listening on this address)

how shoud I set reverse DNS to be trusted and nat fall to spam?