The Sender field inherits sender StructuredField and handles the Sender: header field in the email.
Sending sender to a mail message will instantiate a Mail::Field object that has a SenderField as its field type. This includes all Mail::CommonAddress module instance metods.
Only one Sender field can appear in a header, though it can have multiple addresses and groups of addresses.
mail = Mail.new mail.sender = 'Mikel Lindsaar <mikel@test.lindsaar.net>' mail.sender #=> 'mikel@test.lindsaar.net' mail[:sender] #=> '#<Mail::Field:0x180e5e8 @field=#<Mail::SenderField:0x180e1c4 mail['sender'] #=> '#<Mail::Field:0x180e5e8 @field=#<Mail::SenderField:0x180e1c4 mail['Sender'] #=> '#<Mail::Field:0x180e5e8 @field=#<Mail::SenderField:0x180e1c4 mail[:sender].encoded #=> "Sender: Mikel Lindsaar <mikel@test.lindsaar.net>\r\n" mail[:sender].decoded #=> 'Mikel Lindsaar <mikel@test.lindsaar.net>' mail[:sender].addresses #=> ['mikel@test.lindsaar.net'] mail[:sender].formatted #=> ['Mikel Lindsaar <mikel@test.lindsaar.net>']