Email Bcc Recipients Not Hidden Using Python Smtplib

This works OK, EXCEPT that the Bcc email addresses are not hidden. How do I hide them? Edit: This question appears to have been asked before, but none of the answers specifically a

Solution 1:

smtplib doesn't include any headers automatically you must explicitly create them.

header = 'To:' + to + '\n' + 'From: ' + user + '\n' + 'Subject:testing \n'