The companies centralized DNS server, I will refer to it as the local DNS, maintains the current table using updates, etc. Zone transfers only occur between the mail bastion host and the local DNS server, and yes the entire table. "Local DNS" is sort of an oxymoron.
Generally speaking, domains for which a company will be permitted to do a zone transfer are unlikely to be large sources of spam.
You're probably thinking of a caching dns server...
Master DNS servers are really the only place changes are done and when they are rebuilt, the serial number changes and that should trigger a transfer on the secondary servers.
Companies/ISPs maintain the primary and secondary servers. Anyone can create a caching DNS server to hold information it requests from domains which is is not SOA (start of authority).
This is something which is not uncommon on inbound email relays for locations with substantial volume of email.
I was using "local DNS" meaning a local (intra autonomous system caching DNS server), as opposed to an "ISP DNS" meaning an DNS server that is beyond my control (extra autonomous system caching DNS server), or the "master DNS" you described.
LOL, all of this has made me realize how wholly inadequate our language is when dealing with technology. A "server" used to mean a person who brought food to your table, A "computer" used to mean a mathematician who performed complex calculations for his employer.