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Can someone tell me when and why a client, MTA relay, Unix .Forward, anonymous relay, or listserver will create, or alter these headers:

  • Resent-Sender:
  • Resent-From:
  • Sender:
  • From:

If you can please include a software version, or an example of software that alters any of those fields.

Finally is it correct to say that the Purported Responsible Address is "dynamic"? (see page 13 here)

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up vote 2 down vote accepted

The following information on message headers comes from Microsoft's information on SenderID


  • This is the preferred header for mailing list software to use. Also the servers that unauthenticated guests use (on a hotel network for example) should post their address here.


  • Third party mailing lists, "email this article to a friend", and similar services that send email on behalf of users use this field.

  • Most of today's mailing list software already adds a header, usually "Sender, that identifies the owner of the mailing list.


  • This header is used by default when a user in one domain sends email to a user in another.

None of the above

  • Unix .forward configurations don't change anything within the email and make it impossible to distinguish from a spoofer. These systems should use the Resent-from header, or Sender header.

In addition to the headers mentioned above, Microsoft proposed a new envelope command called Mail Submitter that would work alongside the traditional Mail from command

(This is a Community Wiki Post, please edit or update with correct information as you come across it)

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