class Mail::Message

def smtp_envelope_to( val = nil )

mail.smtp_envelope_to #=> ['mikel@test.lindsaar.net', 'lindsaar@test.lindsaar.net']
mail.smtp_envelope_to ['Mikel ', 'Lindsaar ']

Example:

Also allows you to set the value by passing a value as a parameter

mail.smtp_envelope_to #=> 'mikel@test.lindsaar.net'
mail.smtp_envelope_to = 'Mikel '

Example:

Defaults to #destinations: To, Cc, and Bcc addresses.

Returns the SMTP Envelope To value of the mail object. 
def smtp_envelope_to( val = nil )
  if val
    self.smtp_envelope_to = val
  else
    @smtp_envelope_to || destinations
  end
end