Automatically Bcc an Address on Every Message in Mac OS X Mail

If you are using our email dropbox feature with Mac OS X Mail you may want to automatically BCC your dropbox with every email. The following steps work, but please make sure you see the warning at the bottom of this article.

To auto-Bcc a copy of every message you send from Mac OS X Mail to a particular email address.

  • Open Terminal.
  • Type “defaults read UserHeaders”.
  • Press Enter.
  • If that command returns “The domain/default pair of (, UserHeaders) does not exist”:
  • Type “defaults write UserHeaders ‘{“Bcc” = “bcc@address”; }'” (excluding the outermost quotation marks) and replace bcc@address with the address you want to be used for the automatic copy.
  • If the “defaults read” command above returns a line of values that starts with “{” and ends in “}”:
  • Highlight the entire line. It might read something like {Reply-To = “reply-to@address”; }, for example.
  • Press Command-C.
  • Type “defaults write UserHeaders ‘” (excluding the outer quotation marks).
  • Press Command-V.
  • Type “‘”.
  • Insert ‘”Bcc” = “bcc@address”; ‘ in front of the closing “}” character, replacing bcc@address with the email address you want to be used for automatic Bcc.
  • The line might now read defaults write UserHeaders ‘{Reply-To = “reply-to@address”; “Bcc” = “bcc@address”; }’, for example.
    Press Enter.


Unfortunately, this neat trick has a major drawback. Mac OS X Mail will replace any Bcc: recipients you have added to a message while composing it with your default Bcc: address.

If you want to add a Bcc: recipient different from the automatic one, you either have to set it via Terminal as above (separate multiple addresses by comma) or remove Bcc from your UserHeaders (make sure you quite Mac OS X Mail before any change) before sending the message.

Disable Automatic Bcc in Mac OS X Mail

To turn off automatic Bcc emails again in Mac OS X Mail:

  • Execute “defaults delete UserHeaders” at the Terminal command prompt to delete all custom headers
  • or set UserHeaders back to what it was before you added “Bcc”.

This article was originally published here, but has been reposted on the Kazeli support center for our clients convenience: