It's most important that there be a PTR record in the first instance. Since most ISP allocated home IP addresses don't have PTR records, many email admins reject email from mail servers whose IP doesn't have a PTR record.
It's best if the PTR record matches exactly the A record, since some email admins will reject inbound email from servers with an A/PTR mismatch.
And it's ideal if the server's HELO, A and PTR records all have the same fqdn!
Hope that helps,
Mark
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___________________________________ L. Mark Stone, CIO  "Uptime. All the time."
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