Header Message-ID is missing

Hello,

We are facing an issue with your module WP Mail Bank.
Google is now verifying the header Message-ID on all received emails. If not present, the email is rejected.
Your module is supposed to support it … but there’s a bug and the header is not present.

To fix the issue, I had to set the mail variable “message_id” to true, so that Zend lib generated a Message-ID.
Before, it was NULL (and the lib does not generate it).

I have the last version of the plugin (4.0.14).

Could you fix this issue ?

Thanks
Best regards,