Hey Tom, glad to hear that did the trick! I have seen this once before in my own testing (Intrusion Detection Block) but wasn't able to replicate in-house to get a task escalated. Can I have you submit a ticket on this so we can take a look with you? In the meantime, adding an entry for that IP to Settings>Security>Whitelist with the Bypass IDS Brute Force toggle enabled - that should help keep your users in good shape in the meantime.
Kyle Kerst
Lead Internal Network/System Administrator
SmarterTools Inc.
smartertools.com