Original Author: Robert Mitchell - Posted June 5th 2015
Apparently this morning, MX Logic made a change that is causing this issue. They are having major issues with this today; this filter is ahead of their whitelist, so there is no relief for us. We've tried different sending IP addresses, but it looks they allow about 100 emails per day per IP address before the block is placed..
They did provide us with steps the recipient can take on their end to disable the filter:
1. Log on to the Control Console
2. Select Email Protection
3. Select Policies
4. Highlight the desired inbound policy (usually Default Inbound) and click Edit
5. Click the Spam tab, this will default to the Classifications sub tab
6. Disable the checkbox for "Enable spam flood prevention"
7. Click Save
Please allow 20 minutes for full replication of the settings across our servers.