User exceeded the maximum of 250 objects of type "objtMessage".

I have users that are regularly exceeding 250 objtMessage objects in Exchange 2010. What this really means is that the user has over 250 Messages open at once. While this seems high, when you consider third party tools and other such things, 250 is really not that much. I actually have a couple of users that regularly spike over 500 on a daily basis.

Whenever this behavior exhibits itself, it's in the form of ERROR in the Application log with EventID 9646. The text reads:

Mapi session "64807ed0-b1b3-4938-92e3-b9dbd9cfe67b: /o=Company/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=User Name" exceeded the maximum of 250 objects of type "objtMessage".

The default setting for this (and other open item limits in Exchange 2010) is detailed in Microsoft's Exchange Store Limits article.

To change from the default settings, open the registry on your Mailbox Server, and navigate to the following key:
HKLM\SYSTEM\ConcurrentControlSet\services\MSExchangeIS\ParametersSystem\MaxObjsPerMapiSession

Update/create the DWORD named objtMessage and give it the decimal value that you need (up it to 500).

Don't forget if you are in a DAG to repeat the registry entries on all Mailbox Servers.

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Dustin Shaw
VCP