Re: undisclosed-recipients

["Adam Sjøgren" <asjo@koldfront.dk>]

Uwe writes:

>> I always thought it was added automatically by a MTA somewhere if you
>> left the To: field blank. I don't think anyone types it in there manually.
>
> Well not gnus.

Like Eric Abrahamsen, I think that this bogus value
"undisclosed-recipients" is inserted by Microsoft Exchange, Gmail or
similar, when there is no To: field.

To test this, I tried composing an email in the Gmail web-interface with
two recipients in Bcc: and nowhere else. The resulting emails arrived
with:

  From: Adam Sjøgren <[redacted]@gmail.com>
  Subject: Test Bcc only from Gmail
  To: undisclosed-recipients:;
  Date: Sun, 10 Feb 2019 19:06:20 +0100

  From: Adam Sjøgren <[redacted]@gmail.com>
  Subject: Test Bcc only from Gmail
  To: undisclosed-recipients:;
  Date: Sun, 10 Feb 2019 19:06:20 +0100

So Gmail inserts the bogus value "undisclosed-recipients:;" in To: when
you only put recipients in the Bcc field and leave To and Cc empty.

Let's try the same from outlook.com:

  From: Adam Sjøgren <[redacted]@outlook.com>
  Subject: This is a test of Bcc only from Outlook.com
  Date: Sun, 10 Feb 2019 18:17:07 +0000

  From: Adam Sjøgren <[redacted]@outlook.com>
  Subject: This is a test of Bcc only from Outlook.com
  Date: Sun, 10 Feb 2019 18:17:07 +0000

So at least one part of Microsoft doesn't.

Let's try from some smaller players; Tutanota:

  From:  <[redacted]@tutanota.com>
  Subject: Bcc only from Tutanota
  Date: Sun, 10 Feb 2019 19:22:59 +0100 (CET)

  From:  <[redacted]@tutanota.com>
  Subject: Bcc only from Tutanota
  Date: Sun, 10 Feb 2019 19:22:59 +0100 (CET) (10 minutes, 42 seconds ago)

nope; but Protonmail does, emulating Google:

  From: Adam Sjøgren <[redacted]@protonmail.com>
  Subject: Bcc only from ProtonMail
  To: undisclosed-recipients:;
  Date: Sun, 10 Feb 2019 18:27:28 +0000
  Reply-To: Adam Sjøgren <[redacted]@protonmail.com>

  From: Adam Sjøgren <[redacted]@protonmail.com>
  Subject: Bcc only from ProtonMail
  To: undisclosed-recipients:;
  Date: Sun, 10 Feb 2019 18:27:28 +0000
  Reply-To: Adam Sjøgren <[redacted]@protonmail.com>

Yahoo! Mail doesn't:

  From: Adam Sjøgren <[redacted]@yahoo.com>
  Subject: Bcc only from Yahoo! Mail
  Date: Sun, 10 Feb 2019 18:28:54 +0000 (UTC)
  Reply-To: Adam Sjøgren <[redacted]@yahoo.com>

  From: Adam Sjøgren <[redacted]@yahoo.com>
  Subject: Bcc only from Yahoo! Mail
  Date: Sun, 10 Feb 2019 18:28:54 +0000 (UTC)
  Reply-To: Adam Sjøgren <[redacted]@yahoo.com>

And neither does Aol Mail (guess they are the same these days, at least
the email sent from Aol Mail was delivered by a yahoo.com-host):

  From:  <[redacted]@mcom.com>
  Subject: Bcc only from Aol Mail.
  Date: Sun, 10 Feb 2019 18:31:17 +0000 (UTC)

(I'm too lazy to wait for the other one to arrive; I've got greylisting
on.)


Why do you find it attractive to have this value in To:‽


  Best regards,

    Adam

-- 
 "I pragmatically turn my whims into principles!"             Adam Sjøgren
                                                         asjo@koldfront.dk