Hi, We're seeing occasional 9646 errors: Log Name: Application Source: MSExchangeIS Date: 27/06/2012 09:57:38 Event ID: 9646 Task Category: General Level: Error Keywords: Classic User: N/A Computer: SERVER001.uk.domain.com Description: Mapi session "guidstuff: /o=stuff/ou=UK-Mailbox/cn=Recipients/cn=Blokey" exceeded the maximum of 32 objects of type "session". now, they're not very often, and i know i can follow the instructions below to increase the session limit to 64, or 128. http://technet.microsoft.com/en-us/library/ff477612.aspx i am, however, aware of Neil Hobson's advice below that increasing the limit without understanding why is merely hiding the problem. http://social.technet.microsoft.com/Forums/en/exchangesvrgeneral/thread/36c11ba1-e779-4ee3-bea6-6ddf07c9e2c8 I wouldn't just go changing the registry key as this is simply masking the problem. Go to the user in question and see what they're doing. Last time we saw this it was due to the user's Outlook client having the "download shared folders" option enabled like Raj said earlier, causing shared mailbox contents being downloaded locally. Also, the other thing that often causes this is when the user has 3rd party desktop search programs enabled, hammering the server, etc. Neil Hobson, Exchange MVP Now, i've read a lot of Neil's stuff and i certainly wouldn't dismiss what he has to say, so we went to check the user and.. nothing. The user doesn't have third party apps, doesn't have blackberry, isn't opening lots of shared folders. doesn't appear to be misbehaving in any way. so we did some more digging, and looked at get-logonstatistics. we could see 30 connections for this user into the store. 3 of them were client=MSExchangeRPC, and 27 of them were Client=CI. that seemed pretty odd, but we came across this article: http://blogs.technet.com/b/exchangesearch/archive/2011/05/17/get-logonstatistics-shows-logons-to-a-mailbox-on-the-active-node-by-the-exchange-search-indexer-on-the-passive-node-s-of-a-dag-in-exchange-2010.aspx which explains perfectly why Content Indexing makes connections into the store, and why they are under the user's logon, but it leaves these two questions unanswered: 1. why are there so many connections made by Content Indexing? 2. Do these connections count toward the user's session limit?