Our Microsoft Exchange server Std 2010 has operated with no issues up until recently. Delays occur any time during the day but mostly between 10:00 and 14:00. A day or two may go by where the system is fine though. CPU Utilization normally increases to 100% when delays occur and the NT Kernel System service runs very high.
The server runs as a virtual domain controller and an Exchange Server using Windows 2008 R2 and works together with another SMTP virtual server having GFI Mailessentials 2014 (latest build). Both servers run on Vmware 5.1 and have what we believe to be sufficient resources. There are approximately 250 mail users. A third server runs GFI Mailarchiver that interfaces with the active directory.
Servers have the latest Windows patch releases and Exchange SP3.
There is no antivirus applications running on the servers.