Network and addresses
PTR (reverse record)
A name tied to an IP address. A mail server needs it so mail does not land in spam.
A regular DNS record leads from a name to an address, while PTR goes the other way, from an address to a name (for example, mail.example.com). It is set by the address owner, i.e. the provider — usually on request or in the panel.
Mail servers check the sender's PTR: without it mail often lands in spam. If your VPS will send mail, ask the provider to set up a reverse record.