What is a CNAME record?
A CNAME record makes one name an alias for another: every lookup for the alias is answered with the records of its target, the canonical name. Providers ask for them to point a subdomain at their service, as in DKIM keys or tracking links. RFC 2181 section 10.1 allows an alias no other records of its own.
Reading the result
The chain is listed hop by hop, each with its TTL, ending at the name that holds the actual records and the addresses found there. A name that is not an alias says so, which is the answer when a provider asked you to add a CNAME and it has not appeared yet.
Beat runs on the same engine, on a schedule, across all 41 checks and 25 blacklists. What it adds is asking again, noticing when an answer changes and telling you what to do about it.
Common problems it finds
A dangling CNAME
The chain ends at a name that does not exist. If that name sits on a service where anyone can register it, whoever does can serve content under your subdomain. Remove the record or point it at a name you control.
A loop
Two aliases that point at each other, or a longer circle, never reach an address. Resolvers give up and nothing using the name works.
A CNAME at the domain itself
The top of a zone must hold SOA and NS records, which a CNAME cannot sit beside. Mail lookups then follow the alias to another domain’s MX.
Other records beside the CNAME
A TXT or MX record at the same name as a CNAME breaks RFC 2181, and what resolvers return depends on their software. Keep one or the other.