Sending out an email to multiple contacts should use BCC field instead of To: field

When you do a search on multiple contacts and use "Send Email to Contacts" action, the email will have multiple addresses in "To:" field. Receiving an email with bloated to field is usually very badly percepted and sometimes drives to unpleasant situations where everyone is replying to everyone with unsubscription requests and all kinds of flames. The solution for this would be to always put multiple addresses in "Bcc:" header instead of "To:" header.