This is the error which prompted the server to reboot:

Log Name:      System

Source:        Microsoft-Windows-WER-SystemErrorReporting

Date:          3/1/2015 9:27:00 PM

Event ID:      1001

Task Category: None

Level:         Error

Keywords:      Classic

User:          N/A

Computer:      exch13-02.domain.com

Description:

The computer has rebooted from a bugcheck.  The bugcheck was: 0x000000ef (0xffffe000f9bfc080, 0x0000000000000000, 0x0000000000000000, 0x0000000000000000). A dump was saved in: C:\Windows\MEMORY.DMP. Report Id: 030115-27921-01.

Event Xml:

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">

  <System>

    <Provider Name="Microsoft-Windows-WER-SystemErrorReporting" Guid="{ABCE23E7-DE45-4366-8631-84FA6C525952}" EventSourceName="BugCheck" />

    <EventID Qualifiers="16384">1001</EventID>

    <Version>0</Version>

    <Level>2</Level>

    <Task>0</Task>

    <Opcode>0</Opcode>

    <Keywords>0x80000000000000</Keywords>

    <TimeCreated SystemTime="2015-03-02T05:27:00.000000000Z" />

    <EventRecordID>36389</EventRecordID>

    <Correlation />

    <Execution ProcessID="0" ThreadID="0" />

    <Channel>System</Channel>

    <Computer>exch13-02.SC.ESILICON.com</Computer>

    <Security />

  </System>

  <EventData>

    <Data Name="param1">0x000000ef (0xffffe000f9bfc080, 0x0000000000000000, 0x0000000000000000, 0x0000000000000000)</Data>

    <Data Name="param2">C:\Windows\MEMORY.DMP</Data>

    <Data Name="param3">030115-27921-01</Data>

  </EventData>

Hi,

It seems like a Windows Server problem, not an Exchange Server problem.

Whats the version of your Windows Server and Exchange Server?

Similar thread:

https://social.technet.microsoft.com/Forums/en-US/f132d246-7114-4223-9ff7-e72f3ade0708/exchange-server-2013-restarts-frequently-after-cumulative-update-3-is-installed?forum=exchangesvradmin

Best Regards.

you might find some additional information here in the link below:

http://itsalwaysmyproblem.com/2013/08/27/exchange-2013-and-bugcheck-0x000000ef/