It depends on the MX you're delivering mail to. Some aren't restrictive at all, some will reject if there's an A/PTR mismatch, etc. I make use of FCrDNS on my m

It depends on the MX you're delivering mail to. Some aren't restrictive at all, some will reject if there's an A/PTR mismatch, etc. I make use of FCrDNS on my mail systems.