SourceOne Email Management: OWA Shortcut Add-in server error in application

Summary: SourceOne OWA Shortcut Add-in returning Server Error when attempting to view original items, HTTP 500 response

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Symptoms



When Attempting to view original items using the SourceOne OWA Add-in it in an Exchange environment using an NLB that does not have affinity configured the following error occurs:
Server Error in '/owa/ES1OWA2016' Application

Viewing the IIS logs indicates the site request failed with a HTTP 500 response.
Nothing is logged in any of the SourceOne OWA ES1OWA2016 logs.

The IIS Trace log reports the following:
Server Error in '/owa/ES1OWA2016' Application.

Validation of viewstate MAC failed. If this application is hosted by a web farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

IIS Trace logging can be enabled and viewed using the following:

Go To: Default Web Site/owa/ES1OWA2013Web
using Features view
1. select configuration editor
2. expand system.web in the Section drop-down
3. select  trace  from under the system.web tree
    set these:
    enabled=true
    localonly=true
    mostrecent=true
    pageoutput=true
    requestlimit=10
    tracemode=sortbytime
    writetodiagnostics=true
4. Apply changes

Make the request that fails and then go to browser
http://localhost/owa/ES1OWA2016/trace.axd

Cause

This issue is caused by the cryptographic key used for the application being different between the application servers which causes request failures.  See the following Microsoft KB for complete details:
https://support.microsoft.com/en-us/help/2915218/resolving-view-state-message-authentication-code-mac-errors

Resolution

1. Enabled server affinity on the NLB to ensure all traffic for a requesting client is handled by  a single server.
2. Set a common machineKey value on all ES1OWA2016 sites to ensure that all requests to each server can be fulfilled successfully.
IIS 7 allows the automatic creation of a custom machine key, once configured on the first site use those values on all other ES1OWA2016 sites.  The following sites provide instructions on creating and using machineKey:

https://blogs.msdn.microsoft.com/vijaysk/2009/05/13/iis-7-tip-10-you-can-generate-machine-keys-from-the-iis-manager/

https://support.microsoft.com/en-us/help/2915218/resolving-view-state-message-authentication-code-mac-errors

Once configured the machineKey value will be present in the web.config file within the system.web tree:

<machineKey decryptionKey="VALUE" validationKey="VALUE" />

Affected Products

SourceOne Email Management

Products

SourceOne, SourceOne Email Management
Article Properties
Article Number: 000050309
Article Type: Solution
Last Modified: 10 Sep 2025
Version:  6
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