IMAP connection settings and workload management on Exchange 2013


One of my Exchange 2013 customers currently running Exchange 2013 CU2v2 started to have problems with IMAP connections to his server. IMAP log stated, that conection limit has been reached:

IMAP_Connection_limit_reached

I have examined IMAPSettings from Exchange management shell, and here it is. Connection limit per user is set to 16 by default and counters are reset after 240000 milliseconds (4 minutes), which is not enough. First part of this article will be about the possibilities how to set IMAP from connection point of view. Second part is, how to deal with IMAP in case server is under heavy load and it is expected to have IMAP running.

1. IMAP Settings from connection point of view

IMAP connections limits can be set in levels of MaxConnections, MaxConnectionFromSingleIP, MaxConnectionsPerUser. First two limits are very high, but third limit is set to 16 by default and throttling policy let counter reset after 240000 milliseconds by default, which means, that if user make more than 16 connections in 4 minutes, he is banned till next counter reset.

imap limit

So connection limit might be increased by the following command:

Set-IMAPSettings -MaxConnectionsPerUser <Number>
Get-Service *IMAP* | Restart-Service

Result can be seen on the Picture below (Reset of IMAP services must be made):

IMAP_User_connection_setting

imap limita

Details about settings are here: http://technet.microsoft.com/en-us/library/aa998252(v=exchg.150).aspx

2. IMAP settings from Workload management point of view

Limits per user are set and now I would need to fulfill customer needs if server load is increased. In my case customer needs to have IMAP working properly even there is high utilization of system resources. First I went to Technet web link http://technet.microsoft.com/en-us/library/jj150485(v=exchg.150).aspx and selected the best suitable Workload Classification for my customer. Default Workload Classification for IMAP is Internal Maintenance. If one of performance indicators is in Overloaded or pass the Critical threshold, IMAP service might be temporarily inaccessible for users (Monitored system resources are described in the Technet article as well).

So in this stage I have checked tables and according the server utilization I suggested to increase Workload Classification from Internal maintenanace (Picture below) to Customer Expectation, which means, that even the server will be under heavy load, IMAP is going to work for users.

Before Setting (Default Workload Classification):

IMAP_Connection_limit_Workload_management_before

After setting performed by the following command:

Get-WorkloadPolicy IMAP | Set-WorkloadPolicy -WorkloadClassification CustomerExpectation

IMAP_Connection_limit_Workload_management_after Done!

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