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What hostname should be specified in PTR record?
Note: PTR record should be configured on ISP side.
The main requirement for PTR is that the hostname, which is specified in the PTR record for IP address will be able to resolve to the same IP address.
For example, if example.com is specified in PTR for 203.0.113.2, there should be A record for example.com which contains 203.0.113.2 address.
The following conventions are usually applied to PTR records:
- There should be exactly one PTR record per IP address/name pair. Each IP address should have a PTR record. Note that this isn’t one PTR record per computer, necessarily; a computer with multiple IP addresses would have multiple PTR records, one per address. If one address has multiple names (real A-Records, not CNAME alias), there will be one PTR record per name/address pair.
- For any given MX record, the mailhost name used in the MX record must have an A record - this is the rule, not a convention. The convention is, that name’s IP address must have a PTR record that resolves back to the name used in the MX record.
- There should be an A record for every PTR record (but not necessarily vice versa). In other words, one should be able to take an IP address, look up its PTR record (yielding a hostname), and then look up the A record for that hostname and get back the IP address. The hostname should have exactly one A record (not a CNAME record).