Is there a way to make postal use IPv4 as a fallback if IPv6 Softfails

[prabhu-ninja]

I got a the following error message when sending via IPv6. The postal softfails on the message and tries it again until it hardfails

450 4.7.25 Service unavailable, sending IPv6 address [IPv6-IP] must have reverse DNS record (S820). [wwwwwwww.namprd05.prod.outlook.com 2025-08-04T05:51:48.520Z 08DDD039ED57502D]

The issue appears to be strange because the PTR records (reverse DNS) have been set and checked for propagation across the globe using various tools, but not sure why it is not picked up by outlook servers alone

The question here is. Is there a way to make postal choose the configured IPv4 as a fallback in this case and send the message?

[willpower232]

I'm not sure its possible because I don't think it is actively choosing which to use, 4 or 6, I think its just using whatever connection it can.

[prabhu-ninja]

@willpower232 Thank you for the response. Appreciate it!

What I observed was Postal picks IPv6 if the destination server supports it and IPv4 if it does not. I would like to leverage IPv6, so switching to IPv4 alone for this case, though an alternative, feels like we are not using the potential available. :)

Reverse DNS not propagating to a set of Outlook servers is not in our control to fix, so thought if we can do something with Postal as a workaround.

Will check for other options.