EWS Basics Accessing and using Shared mailboxes

One of the most commonly asked and misunderstood things that people starting out using Exchange Web Services get wrong is accessing a Shared Mailbox or a Delegated Mailbox other then that of security principal (another way of saying credentials) you are authenticating with.

Autodiscover

One of the first confusion points is with Autodiscover, for people who aren't that familiar with Exchange its important to understand that all Autodisover does is gives you the endpoint to connect to for Exchange Web Services. Some people confuse using the following line

$service.AutodiscoverUrl("Mailbox@domain.com",{$true})

To mean all future EWS requests will go the mailbox you use here which isn't the case all this will do is return the most optimized endpoint for EWS request for that particular user.

Authentication

By default nobody has access to a Mailbox other then the owner of that mailbox, a common problem that people have is to believe they can use the admin account to access any users Mailbox content .  Access to a Mailbox needs to be granted via

• Adding the user as a Delegate in Outlook or via the EWS Delegate operations
• Giving the user full access using Add-MailboxPermission in the Exchange Management Shell
• Grant EWS Impersonations rights on the Mailbox via the Application Impersonation RBAC role
• Give Access to particular mailbox folder in Outlook or via Add-MailboxFolderPermssion

Accessing a Shared Mailboxes folder

To Access a Mailbox folder in EWS you need to know the EWSId of the folder, the one exception to this rule are the WellKnownFolders like the Inbox,Contacts,Calendar etc. With these WellKnowFolders you can tell EWS which folder you want in which mailbox without knowing the EWSId of that folder.

Eg to Access the Inbox in a Shared Mailbox you use the FolderId overload to define the folderId you want to access and then bind to that folder

$folderid= new-object Microsoft.Exchange.WebServices.Data.FolderId([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::Inbox,$MailboxName) 
$Inbox = [Microsoft.Exchange.WebServices.Data.Folder]::Bind($service,$folderid)

If its a user created folder you want to access then this is where some complexity comes in, to access the folder you need to get the EWSId of that folder. The easiest way to do this would be to search for that folder within the target mailbox, however depending on what rights you have that this may or may not be a problem. But if you do have Full access or Impersonation rights to a Mailbox then to access a usercreated folder turn the folder you want to access into a path like \\Inbox\folder1\folder2 and you can then use a function like this

function Get-FolderFromPath{
 param (
   [Parameter(Position=0, Mandatory=$true)] [string]$FolderPath,
   [Parameter(Position=1, Mandatory=$true)] [string]$MailboxName,
   [Parameter(Position=2, Mandatory=$true)] [Microsoft.Exchange.WebServices.Data.ExchangeService]$service,
   [Parameter(Position=3, Mandatory=$false)] [Microsoft.Exchange.WebServices.Data.PropertySet]$PropertySet
    )
 process{
  ## Find and Bind to Folder based on Path  
  #Define the path to search should be seperated with \  
  #Bind to the MSGFolder Root  
  $folderid = new-object Microsoft.Exchange.WebServices.Data.FolderId([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::MsgFolderRoot,$MailboxName)   
  $tfTargetFolder = [Microsoft.Exchange.WebServices.Data.Folder]::Bind($service,$folderid)  
  #Split the Search path into an array  
  $fldArray = $FolderPath.Split("\") 
   #Loop through the Split Array and do a Search for each level of folder 
  for ($lint = 1; $lint -lt $fldArray.Length; $lint++) { 
         #Perform search based on the displayname of each folder level 
         $fvFolderView = new-object Microsoft.Exchange.WebServices.Data.FolderView(1) 
   if(![string]::IsNullOrEmpty($PropertySet)){
    $fvFolderView.PropertySet = $PropertySet
   }
         $SfSearchFilter = new-object Microsoft.Exchange.WebServices.Data.SearchFilter+IsEqualTo([Microsoft.Exchange.WebServices.Data.FolderSchema]::DisplayName,$fldArray[$lint]) 
         $findFolderResults = $service.FindFolders($tfTargetFolder.Id,$SfSearchFilter,$fvFolderView) 
         if ($findFolderResults.TotalCount -gt 0){ 
             foreach($folder in $findFolderResults.Folders){ 
                 $tfTargetFolder = $folder                
             } 
         } 
         else{ 
             Write-host ("Error Folder Not Found check path and try again")  
             $tfTargetFolder = $null  
             break  
         }     
     }  
  if($tfTargetFolder -ne $null){
   return [Microsoft.Exchange.WebServices.Data.Folder]$tfTargetFolder
  }
  else{
   throw ("Folder Not found")
  }
 }
}

Once you have the EWSId of the Folder you can use that in FindItems Operation or another other EWS operation that takes a FolderId to do what you want. For Example

Sending Email As a Shared Mailbox

To send a message as another user you need to first have either SendAS permissions to that Mailbox or Send on Behalf off (the latter will mean the message will be marked as Sent On Behalf)

The first thing in you code you want to do is bind to the SentItems folder of the Mailbox you want to send as eg

$folderid= new-object Microsoft.Exchange.WebServices.Data.FolderId([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::SentItems,$MailboxName)   
$SentItems = [Microsoft.Exchange.WebServices.Data.Folder]::Bind($service,$folderid)

Then when you create a message to Send set the From address to the Mailbox you want to SendAs and set the SentItems FolderId to the Target mailbox so a copy of what you will be sending will be saved to the SentItems folder of that mailbox eg

function Send-EWSMessage  {
     param( 
             [Parameter(Position=0, Mandatory=$true)] [string]$MailboxName,
  [Parameter(Mandatory=$true)] [System.Management.Automation.PSCredential]$Credentials,
  [Parameter(Position=2, Mandatory=$false)] [switch]$useImpersonation,
  [Parameter(Position=3, Mandatory=$false)] [string]$url,
  [Parameter(Position=6, Mandatory=$true)] [String]$To,
  [Parameter(Position=7, Mandatory=$true)] [String]$Subject,
  [Parameter(Position=8, Mandatory=$true)] [String]$Body,
  [Parameter(Position=9, Mandatory=$false)] [String]$Attachment
                )  
  Begin
 {
  if($url){
   $service = Connect-Exchange -MailboxName $MailboxName -Credentials $Credentials -url $url 
  }
  else{
   $service = Connect-Exchange -MailboxName $MailboxName -Credentials $Credentials
  }
  if($useImpersonation.IsPresent){
   $service.ImpersonatedUserId = new-object Microsoft.Exchange.WebServices.Data.ImpersonatedUserId([Microsoft.Exchange.WebServices.Data.ConnectingIdType]::SmtpAddress, $MailboxName) 
  }
  $folderid= new-object Microsoft.Exchange.WebServices.Data.FolderId([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::SentItems,$MailboxName)   
  $SentItems = [Microsoft.Exchange.WebServices.Data.Folder]::Bind($service,$folderid)
  $EmailMessage = New-Object Microsoft.Exchange.WebServices.Data.EmailMessage -ArgumentList $service  
  $EmailMessage.Subject = $Subject
  #Add Recipients    
  $EmailMessage.ToRecipients.Add($To)  
  $EmailMessage.Body = New-Object Microsoft.Exchange.WebServices.Data.MessageBody  
  $EmailMessage.Body.BodyType = [Microsoft.Exchange.WebServices.Data.BodyType]::HTML  
  $EmailMessage.Body.Text = "Body"  
  $EmailMessage.From = $MailboxName
  if($Attachment)
  {   
   $EmailMessage.Attachments.AddFileAttachment($Attachment)
  }
  $EmailMessage.SendAndSaveCopy($SentItems.Id) 
  
 }
}