Free tool
The A, MX, TXT or NS records of any name, queried from each of its DNS servers.
Reference
A domain publishes its records on its DNS servers. Each type answers a different question: where the website is, where email goes, who can issue certificates.
The types
A and AAAA point to the website's IP; MX, to the server that receives email; TXT holds SPF and service verifications; CNAME makes one name an alias of another. NS says which servers hold the zone and SOA, which one is the primary.
A typical zone
exampleA 203.0.113.10
the website
MX 10 mail.yourdomain.com
incoming email
TXT v=spf1 mx ~all
who sends email
CNAME www > yourdomain.com
www is an alias
CAA issue "letsencrypt.org"
who issues certificates
The TTL
Every record has a TTL: the seconds a resolver can keep the answer before asking again. If you change a record with a TTL of one day, some people will keep seeing the old value for a day.
Common TTLs
300
before a migration
3600
the norm
14400
cPanel default
86400
records that don't change
The authoritative servers
A resolver like your ISP's or 8.8.8.8 gives you what it had stored. We go to the authoritative servers, the ones that hold the zone, and ask each one separately. If one answers differently, the zone hasn't been copied properly and each visitor may see something different. To see what resolvers in different countries answer, use DNS propagation.
MX for yourdomain.com
livens1.theservercluster.com
same answer
ns2.theservercluster.com
same answer
ns3.theservercluster.com
old copy of the zone
It's asking a domain's DNS servers which records it publishes. With it you find out which IP the website points to (A and AAAA records), where email is received (MX), which email verifications and policies it has (TXT) or which servers hold the zone (NS). For email it's also called an MX lookup.
Because your computer asks a resolver that stores answers for each record's TTL. We read from the authoritative servers, which always have the current value. If you've just changed something, you'll see it here straight away and on your computer when the cached copy expires. To see how the change is spreading around the world, check DNS propagation.
Choose MX in the drop-down and type the domain. You'll see each mail server with its priority: the lowest number is tried first, and the others are backups. If the domain has no MX, email sent to it won't arrive anywhere. To change them, follow the guide on changing MX records.
It means not all of the domain's DNS servers have the same copy of the zone. Right after a change it's normal for a few minutes. If it lasts longer, one of them isn't syncing and each visitor sees something different depending on which one they ask. There's one exception: large services spread the load by returning different IPs from each server, and that isn't a problem.
Not according to the standard: the root of the domain must have the SOA, the NS and usually the MX records, and a CNAME can't coexist with other records. Some DNS providers offer an ALIAS record or “flatten” the CNAME so it works; if yours doesn't, use an A record with the IP.
