The entire email. To see the entire email in Gmail, view an email then click the dropdown menu on the far right, and choose "View Original".
The entire header block, which is everything up to a blank line.
Email Header Field
For example the subject header field may be "Subject: Hello World". A header field may span multiple lines. For our programming, we call this the Email Header Field Text.
Email Header Field Name
For example the subject header field name is "Subject"
Email Header Field Body
For example the subject header field body is "Hello World"
A string like "firstname.lastname@example.org". The format of email addresses is defined in RFC 5322 (mostly section 3.4.1) and RFC 5321. Notably the email address can be up to 320 characters long, and can contain some special characters like the "+" plus sign for single account filtering.
Email Address Display Name
An optional string to display in front of an email address. For example the "To" header field may be "To: John Doe <email@example.com>" shows the diplay name "John Doe" then the email address "firstname.lastname@example.org" in angle brackets.
The entire email body block, i.e. everything after the first blank line.
Example Email Header Field
Email Header Field Name: "To"
Email Header Field Body: "John Doe <email@example.com>"
Email Header Field Text: "To: John Doe <firstname.lastname@example.org>"
Email Address: "email@example.com"
Email Address Display Name: "John Doe"
Naming Conventions for Developers
We like to use highly descriptive naming conventions that match the email RFC.