Recently, i sent out a mass email to users using drupal mail function, more concisely, using the mass_contact module in the drupal, and found out that the Bcc contacts were not hidden in Gmail and live mail. But the yahoo mail and other mail client software (mac Mail App) work fine with the bcc field hidden for the same mail generated.

The problem is only stick to php generated mails, for the mails sent from my mac Mail Application, the bcc works fine.

The problem is frustrating and I received complains from users about leaking their email address.

Here is the screen-cap from gmail,

Is there any solution for this situation?