DenyHosts, a software which blocks malicious ssh attempts, is installed by default on all of our managed servers. To check if any authentic hosts are blocked from sshing you can run:
If there are any blocked hosts you will see a section like below (111.222.333.444 is a placeholder IP):
IGPP HelpDesk is automatically notified of any blocked hosts. If you would like to be added to the email list for blocked IPs on your managed server, send a request to email@example.com.