Important Note: Currently there are no known issues with delivery to Optimum, however this may resurface again in the future until Optimum's blacklist enforcement has changed.
Optonline.net or the Optimum internet service provider has implemented IP range blocking for their spam filtering. Optimum has determined that a range of IP addresses within Amazon Web Services (AWS) are always considered spam. This is an aggressive, broad approach to filtering in the new cloud-computing age, and as a result, a few of Mailprotector's servers have fallen within the list.
If IP addresses are on a blacklist, Mailprotector will typically remove the servers from production so they are sending the minimum traffic required to improve the reputation with an email service provider.
After extensive discussions with Optimum, they will not whitelist or remove Mailprotector servers from Optimum's block list. Optimum blocks full ranges of IP addresses instead of individual IP addresses.
Since Optimum continues to take an aggressive approach to spam filtering, Mailprotector is unable to remove servers from production for Optimum delivery problems. If Mailprotector removed IP addresses for Optimum, the IP addresses would be out of production indefinitely.
The only suggested workaround is to have a user resend the email that was blocked. A different server of the thirty-two handling outbound email should be used for delivery. If the server doesn't fall into the IP range Optimum is blocking, the email will deliver as expected.
We apologize for this inconvenience. If you have any questions or concerns, please open up a support request with the Partner Success team. We are always happy to help!