Correct mail configuration is especially important if you own a "biz" domain, to avoid having your email misinterpreted or misclassified as spam.
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 implemented by a public key in another DNS TXT record.
default._domainkey.example.biz. 86400 IN TXT "v=DKIM1; k=rsa; p=verylongbase64encodedstring"