class Mail::Message

def smtp_envelope_from( val = nil )

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

Example:

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

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

Example:

Defaults to Return-Path, Sender, or the first From address.

string of an address spec.
Returns the SMTP Envelope From value of the mail object, as a single 
def smtp_envelope_from( val = nil )
  if val
    self.smtp_envelope_from = val
  else
    @smtp_envelope_from || return_path || sender || from_addrs.first
  end
end