DNS record contains 0.0.0.0 address
It is legal (see RFC1035 §3.4.1), but useless (as it would mean "any IP"). As for the meaning, please have a look at Zoneedit FAQ (which is wrong BTW, there is no mandatory requirement to have an A record on the domain name itself, quite the contrary, all MTAs can use MX records) :
- Why can't I delete the "A" record for the root name of my domain?
All domains must have an "A" record for the root of the domain. Omitting this "A" record may prevent some mail servers from delivering your email correctly. WebParking or WebForwarding the root of your domain is sufficient, because both of these create hidden "A" records pointing to our servers. If you're really looking to delete this record, try changing the IP address to "0.0.0.0" instead, it's functionally equivalent.
Famously it was used to shut down parler.com by the domain registrar epik
$ dig @NS3.EPIK.COM parler.com
; <<>> DiG blah blah blah <<>> @NS3.EPIK.COM parler.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43362
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;parler.com. IN A
;; ANSWER SECTION:
parler.com. 300 IN A 0.0.0.0
The result was to serve an error page from the local web server.