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How to enable Dark mode in Outlook on Web in Office365 with EWS and PowerShell

Last year at Ignite Microsoft announced Dark mode for Outlook On the Web, while this seem to excite a lot of people I never really caught the buzz. However after taking the plunge after being notification bugged by Outlook this week I've found it to be a nice addition especially if your eyes aren't 100%.

When you enable Dark mode using the slider in Outlook on the Web

 
This changes/creates a setting called "isDarkModeTheme" in the OWA.UserOptions User Configuration Object which is held in the FAI collection (Folder Associated Items) in the Non_IPM_Root of the Mailbox. If you want to enable this setting for a user (or users) programmatically or just want to take stock of who is using this then you can use EWS to Read and Set the value in the OWA.UserOptions User Configuration Object in a Mailbox. (if you want to do this in the Microsoft Graph you will need to cry into your beer at the moment because the Microsoft Graph still doesn't support either user configuration objects or accessing FAI Items 😭😭😭). 

 The code to enable dark mode is pretty easy first you need the FolderId for the Non_IPM_Root folder of the Mailbox you want to work with, then bind to the UserConfiguration object which will return the Dictionary from the underlying PR_ROAMING_DICTIONARY property. If Dark mode hasn't been enabled yet then the property shouldn't yet be in the Dictionary but if its is it will either be set to True of False depending on wether its enabled or not. So to Change this all we need is some simple code like the following 

 
        $folderid= new-object Microsoft.Exchange.WebServices.Data.FolderId([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::Root,$MailboxName)   
        $UsrConfig = [Microsoft.Exchange.WebServices.Data.UserConfiguration]::Bind($service, "OWA.UserOptions", $folderid, [Microsoft.Exchange.WebServices.Data.UserConfigurationProperties]::All)
        if ($UsrConfig.Dictionary) {
            if($UsrConfig.Dictionary.ContainsKey("isDarkModeTheme")){
                if($Disable.IsPresent){
                    $UsrConfig.Dictionary["isDarkModeTheme"] = $false
                }else{
                    $UsrConfig.Dictionary["isDarkModeTheme"] = $true                    
                }
               
            }else{
                if(!$Disable.IsPresent){
                    $UsrConfig.Dictionary.Add("isDarkModeTheme",$true)
                }
            }
        }
        $UsrConfig.Update()

I've put together a simple script that wraps the above and Oauth authentication and provides two cmdlets for getting and setting Darkmode for Outlook on the Web for a mailbox. Eg 

 To Get the Current Dark Mode setting use

  Get-DarkModeSetting -MailboxName mailbox@domain.com

 To Enable Dark Mode use

 Set-DarkModeSetting -MailboxName mailbox@domain.com (will return Get-DarkModeSetting after the update)

To disable Dark Mode use

 Set-DarkModeSetting -MailboxName mailbox@domain.com -Disable

 I've put the script up on GitHub https://github.com/gscales/Powershell-Scripts/blob/master/DarkModeMod.ps1 
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All sample scripts and source code is provided by for illustrative purposes only. All examples are untested in different environments and therefore, I cannot guarantee or imply reliability, serviceability, or function of these programs.

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