Duplicate message IDs generate by ezcMailTools

The message ID is constructed from the hostname, current time (precision: second), the process ID and an incremented static variable.

If several mails are sent in the same second using AJAX requests from the frontend each triggering one mail, using the same PHP process the same message ID might be used multiple times since the static variable is obviously reset between the requests. A more random part embedded in the message ID would help here (uniqid(), mt_rand()).