In simple terms
MAIL FROM – Mr.Blue used XYZ post office to send a mail envelope to Mr.Red, and if Mr.Red’s post office cant locate Mr. Red then the envelope can be sent back to XYZ Post office to be returned to Mr.Blue
FROM – This message is FROM Mr.Blue to Mr. Red (Receiver).
Now the technical stuff:
Like the mail envelope which contains the message, An email envelope also contains a message.
- The email envelope will have three pieces of identification information, the host greeting, the “MAIL FROM:” return address and the “RCPT TO:” list of recipient addresses.
- The message content comprises a set of header fields and a body. The body, in turn can be simple text or can be a structured, multi-media “MIME” object of attachments. The set of header fields can be quite extensive, but typically at least include: “Subject:” “Date:” the “To:” and “From:”.
The “MAIL FROM” command specifies the address of the recipient for return notices if any problems occur with the delivery of the message, such as non-delivery notices.
The “From:” header field indicates who is the author of the message.
The technical notation for referring to components of email information is: RFC5321.MailFrom and RFC5322.From according to the IETF RFCs where the field is defined and the specific field being referenced.
All this information can be spoofed. DMARC protects the domain name of the RFC5322:From field against spoofing.