Exchange Service freezing

Hello,

Several times, the Exchange service go unavailable, I had a chance and I recorded some counters, here below a chart describing: # of Exceptions / sec (black),private bytes (blue), working set (red).

I thought it's BackPressure issue, I had it this issue but that day there was no event log (15004,15005) indicating it 

Is there any one could help me on this, troubleshooting ?

Regards,

Yasine

Yasine .NET Developer --------------------------- Please mark this anwser if you find it helpful