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In case there's no reverse ptr for ping -a <ip> or nslookup <ip> to show, you can run ipconfig /displaydns | clip, open a text editor, paste, and search for the IP there. Note that this will work only if the original DNS query was done via the Windows DNS resolver - some apps do their own DNS queries, like newer browsers using DNS-over-HTTPS ...
But a reverse DNS lookup still only provides the the ISP name: cust.static.213-xxx-yyy-zzz.swisscomdata.ch. In that case, it looks like Reverse DNS is working fine, at least from your end. Confirm this with an external Reverse DNS lookup tool to confirm other servers see the same thing. If that finds the reverse DNS entry, then it's possible ...
Reverse DNS lookups are done by checking the pointer (PTR) records. If you wanna do reverse DNS for "1.2.3.4", you have to lookup pointer records for "4.3.2.1.in-addr.arpa". My function takes in an IP address, reverses the order of the octets (i.e. changes it from 1.2.3.4 to 4.3.2.1), and then uses dig to execute the PTR lookup I just described.
55.34.12.in-addr.arpa - reverse zone, contains PTR records for all IP addresses in the range 12.34.55.x; You obviously control the forward zone, but the reverse zone is controlled by whomever owns the IP addressing range (range 12.34.55.224/28 is allocated to AT&T).
The forward DNS entries ("A" records) for windows machines on the domain are populated automatically. However, the reverse DNS entries ("PTR" Records) are not. The reverse lookup zone exists, and I can add entries to it manually, but it doesn't automatically populate. Dynamic updates are enabled for both the forward and reverse zones.
On the other side, in Windows the reverse lookup seems to be pretty much hard-coded (see a related question Globally disable reverse DNS lookup for Kerberos on Windows? The problem is that the reverse lookups not only break the usage of server aliases (CNAMES), but their optional-ity can cause really unexpected and unstable behavior when ...
Not sure about why SSH does it specifically, but if you configure a box to only allow connections from host.xyz.com, anyone can configure a box and call it host.xyz.com, but if you can have a forward DNS entry for host.xyz.com that points to 1.2.3.4 and a PTR for 4.3.2.1.in-addr.arpa that points to host.xyz.com then it's a much better indication that you truly are host.xyz.com.
It does not have to match the domain name on your e-mail address. Some SMTP servers will reject mail if the reverse DNS doesn't match the HELO/EHLO hostname used in the connection. If your mail server's hostname is mail.example.com then your reverse DNS, MX record, HELO/EHLO, and SMTP greeting banner should all be mail.example.com as well. That ...
sshd seems to almost always try to perform a reverse DNS lookup on new connections. For hosts without a PTR entry this causes delays of 5 seconds per query. Sometimes it accepts the connection immediately, sometimes it tries to resolve once, sometimes twice. I observed this using tcpdump port 53 while trying to connect to the server. I have ...
Only Digital Ocean can control the reverse DNS, as the PTR records aren't on your zone, but on an in-addr.arpa. zone controlled by the owner of the IP address. A Digital Ocean Community question has an answer to this: The Reverse DNS is configured automatically from our end based on the droplet’s hostname.