Limit connections to your mail server
The way messaging protocols work on the Internet means that you cannot be sure that, simply by changing the MX records, you will only receive messages from our servers on your server.
To ensure that you only receive secure messages, we recommend that you restrict the arrival of emails from the Email Filtering Service servers only. This operation will further enhance the security of your mail server by making it invisible to the outside world. Do not hesitate to contact the Email Filtering Service support team or your reseller to validate the IP addresses to be mentioned.
You can implement this limitation in your corporate firewall by setting up security rules authorising only Email Filtering Service servers to correspond with your SMTP protocol server.
You can also use your mail server's security functions