You might have received a notification from some of your senders saying that their email was refused by ImprovMX because their domain or IP addresses are listed on Spamhaus.
We check every incoming email we receive against Spamhaus to verify that the sender is not blacklisted. When they are, we refuse the email in order to not lower our sender reputation and maintain a good quality of service for everybody else.
We test the following data when an email is forwarded via ImprovMX:
The IP of the client that connects to ImprovMX
The IP of the domain associated with the sender (test.com when the sender is firstname.lastname@example.org for instance)
The IP of the domain associated with the recipient
We display a different message based on the data tested:
For 1, we display the following message:
571 Your IP is blacklisted on Spamhaus. To best protect our users from spam, we will ignore all incoming emails from you until the matter is resolved.
For 2 and 3, we display the following message:
571 The IP from the domain “example.com” is listed on Spamhaus. To best protect our users from spam, the message has been blocked.
If you believe that Spamhaus blacklisted your IP address or domains by mistake, you can request removal at Spamhaus by following this link