@LoudLemur (Going by the topic subject), if the error is related to PTR record, then the solution is not correct.
The PTR record is set by your VPS provider and not by your DNS provider
PTR record goes by many names - Reverse DNS, rDNS, PTR. Unlike "forward" DNS which looks up something based on the domain name, a "reverse" DNS looks up based on the IP address. And who owns the IP address? The VPS provider. So, you have to change it there.
This means that to fix PTR record issue, you have to fix this in SSDnodes and not in Porkbun or whatever name server you have. If SSDnodes, does not let you set PTR record, you have to ask them by raising a support ticket.
More information at https://docs.cloudron.io/email/#ptr-record