Hello
My ISP Starlink block SMTP port 25 and I'm using IPv6 to connect to my home nas.
I'm looking to use your service Outbound SMTP relay service with my synology home mailserver with IPv6.
Your IPv4 outbound server are know by PTR reverse lookup, but your IPv6 fails reserve lookup.
So the connection does fail from unknown:

connect from unknown[2602:ff23:0:8888:142:b77e:4738:f5f8]
lost connection after CONNECT from unknown[2602:ff23:0:8888:142:b77e:4738:f5f8]

Could you PTR published DNS record for your IPv6 [2602:ff23:0:8888:142:b77e:4738:f5f8]

Thanks
Sincerely.

Alain KERBOULL