A list of header fields (provided as key-value PAIRS) can be used to initialize the object.
Add values to the list of defined values for the FIELDNAME.
VALUES will replace the old values for the FIELDNAME. Returned is the LIST of values after modification.
The OPTIONS are used to initiate a mailer object via Mail::Mailer::new(). Then Mail::Mailer::open() is called with the knowledge collected in this Mail::Send object.