> On May 15, 2019, at 1:29 PM, Peter Fraser <softwareinfo...@gmail.com> wrote: > > I believe what happened is the testing software they used tried to send an > email out using an empty domain and Postfix accepted it. I did it manually to > verify from the commandline > MAIL FROM: <> > RCPT TO: an email address > DATA > Blablabla > . > Postfix queued up this email and sent it out.
Why shouldn't it be sent? If an inbound message fails to be delivered to the user's mailbox, the outgoing bounce MUST have an empty envelope sender address. For the same reason (avoiding loops) the envelope sender address of MDNs (read-receipts and the like) MUST also be <>: https://tools.ietf.org/html/rfc3798#section-3 The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be null (<>), specifying that no Delivery Status Notification messages or other messages indicating successful or unsuccessful delivery are to be sent in response to an MDN. A message disposition notification MUST NOT itself request an MDN. That is, it MUST NOT contain a Disposition-Notification-To header. If an auditor thinks that messages with <> as an envelope sender are invalid, find an auditor who's less clueless. -- Viktor.
