MacMail - read receipt trouble.Stuffed up coding via Terminal!

Can anyone help my please!!

I have a Mac and use MacMail. I tried coding via Terminal to get read receipt for emails. Now I get an permanent error whenever I bcc which reads bcc@example.com followed by a MAILER-DAEMON@yahoo.com error email reading ...

This is a permanent error; I've given up. Sorry it didn't work out.

<bcc@example.com>:

Sorry, I wasn't able to establish an SMTP connection. (#4.4.1)

What have I done?

I put in the following coding in originally:

defaults write com.apple.mail UserHeaders '{Bcc = "bcc@example.com"; "Disposition-Notification-To" = "Heinz Tschabitscher <sender@example.com>"; }'

via this website http://email.about.com/od/macosxmailtips/qt/et_request_recp.htm

I tried the following to remove it but it hasn't worked.

To turn requesting a read receipt for every message back off:

Execute "defaults delete com.apple.mail UserHeaders" at Terminal command prompt to delete all custom headers or set UserHeaders back to what it was before you added "Disposition-Notification-To".

I'd really appreciate any help with this.

Suppose I shouldn't have messed with it in the first place!

Thanks