We normally do not place security notifications on the our web site, but the issue we see now is dangerous. You must act immediately. Please, read Multiple Security Updates Released for Exchange Server – Microsoft Security Response Center.

The updates you need to install are listed here https://support.microsoft.com/en-us/Search/results?query=kb5000871

If you cannot install the security updates immediately but you want to make sure your servers do not get hacked close port 80 and 443 on your firewall to block access. This means that remote users can no longer connect to your Exchange Server but you are protected for the time you need to install the updates.
 
If you need assistance installing the security updates, please Contact Us and we will get back to you.