Correct mail configuration is especially important if you own a "biz" domain, to avoid having your email misinterpreted or misclassified as spam.
The main technologies
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"
If you are going to use DKIM, you also need a "milter" or similar software for your server to sign email headers with a private key corresponding to the public key in the DNS record. See OpenDKIM.
Domain-based Message Authentication, Reporting, and Conformance
_dmarc.example.biz. 86400 IN TXT "v=DMARC1; p=quarantine"
All of the foregoing technologies are implemented as DNS records. To further secure the authenticity of your email, you might consider using DNSSEC on your domain.