Obviously you can only have one reverse DNS (PTR) record per email address, so how do you set up reverse DNS for multiple email domains sharing a single IP?
To set up multiple reverse DNS records is impossible, but there is a solution to the very common problem. The solution is to pick a “main” email address domain and set a reverse DNS record for that, then create an SPF DNS record that says that the other domains are allowed to send email from that domain’s IP.
❗ Tip: There some really handy SPF record generators available on the internet.
❗ Tip: For most people, your ISP is responsible for your reverse DNS records, not the folk that host your DNS.