Sender Policy Framework
SPF is described in RFC 7208 and implemented as a DNS TXT record.
example.biz. 86400 IN TXT "v=spf1 a mx ~all"
Too short a time-to-live (here 86400 seconds) is often taken as an indicator of spammishness. The "biz" tld itself uses 900 seconds, but that can be used to quickly revoke a spammer's domain.
The version was never updated from 1, but other tools were developed to be used in conjunction with SPF.
DomainKeys Identified Mail
DKIM is described in RFC 6376 and implemented by a public key in another DNS TXT record. Here is the general gist of very simple possible example.
default._domainkey.example.biz. 86400 IN TXT "v=DKIM1; k=rsa; p=base64encodedpublickey"
Domain-based Message Authentication, Reporting, and Conformance
_dmarc.example.biz. 86400 IN TXT "v=DMARC1; p=quarantine"