DMARC
Domain-based Message Authentication, Reporting & Conformance
DMARK is an email authentication tool that links an email address with the domain that it is sent from.
DKIM
Domain Keys Identified Message
This email authentication tool adds a DMIK signature to your email. This digital signature tells receiving email servers that your email was authorized by your domain.
SPF
Sender Policy Framework
This email authentication tool is used to prevent people from sending messages from your domain, preventing phishing attacks.