DKIM
Domain Key Identified Mail: DKIM provides a method for validating a domain name identity that is associated with an email message through cryptographic authentication.
DMARC
Domain-based Message Authentication, Reporting & Conformance:, is an email authentication, policy, and reporting protocol.
It builds on the widely deployed SPF and DKIM protocols, adding linkage to the author ('From:') domain name, published policies for recipient handling of authentication failures, and reporting from receivers to senders, to improve and monitor protection of the domain from fraudulent email.
MTA
Mail Transport Agent: handles mail server to server (e.g. other domains).
MDA
Mail Delivery Agent: handles user access to email (e.g. IMAP).
MUA
Mail User Agent: user client to check email (e.g. thunderbird/outlook).
SPF
Sender Policy Framework: Email authentication method designed to detect forging sender addresses during the delivery of the email.