The following sections provide an overview of the syntax used in sendmail and describe some implementation details.
You can follow flag arguments with recipient name arguments unless you run in SMTP mode. In brief, the following format is used for recipient names.
Anything in parentheses is thrown away (as a comment).
Anything in angle brackets (< >) is preferred over anything else. This rule implements the Internet standard that writes names in the form of username <system-name> and sends to the electronic system-name instead of to the human username.
Double quotes (") denote phrases; backslashes (\) denote characters. Backslashes compare otherwise equivalent phrases differently—for example, user and "user" are equivalent, ...