Sender Policy Framework might be what SPF stands for.

I was orginally told "Server Protected From" but I thought of that just now and it seemed suspicious. See also:

• https://tom-jaeschke.blogspot.com/2012/09/some-dns-basics.html
• https://tom-jaeschke.blogspot.com/2014/08/3ds-is-optional.html

I guess A for address and MX for Mail Exchanger. A CName in DNS points a domain name (subdomain) to another domain name (subdomain). C for canonical. TTL is time to live and is a setting for how long an A record, MX record, etc. may be cached. DNS may stand for Domain Name System instead of Domain Name Services.