SMTP send mail, IP problem / Stalwart 0.10

[chrismaster]

First: Never thought setting up a mail-server could be that easy - getting up and running an mailserver with podman in 10 Minutes is incredible.
But I have one problem.
When sending an email, my emails get the ip address from my upstream firewall, so the rDNS check from eg google gives me an error.
smtp;550 [aaa.bbb.ccZ.ddd] The IP address sending this message does not have aPTR record setup, or the corresponding forward DNS entry does notmatch the sending IP. As policy, Gmail does not accept messagesfrom IPs with missing PTR records, for more.....

aaa.bbb.ccZ.ddd/24 is my firewall with a public ip, but my mailserver is aaa.bbb.ccC.ddd/29, also with an public ip behind the firewall in a DMZ. my rdns are set to the mailserver aaa.bbb.ccC.ddd, so rdns checks fail cause they check with my firewall ip.
My Setup:
podman with stalwart 0.10 open ports 25/443/465/993
certificate with letsencrypt TLS-ALPN-01 inside stalwart
I don't get it, why my mails from stalwart think the ip is from the upstream firewall.
Since the installation was so smooth, I might have missed something.
Thx
chris

[chrismaster]

Maybe from interest:
443 is behind haproxy on the same server. But TLS-ALPN-01 got the certificate, so I think the reverse proxy doesn't have to do with the problem.
25, 465, 993 are not behind the reverse proxy.

[chrismaster]

Its a network problem, not a problem with stalwart.
After disabling outbound NAT everything is fine...
Sorry