[Powershell] Get Exchange FolderID

Connect to Exchange Online Powershell

Connect-ExchangeOnline

Run the following Powershell script to get your list of FolderID

# Collect the target email address or SharePoint Url
# Authenticate with Exchange Online and the Microsoft Purview portal (Exchange Online Protection - EOP)
$addressOrSite = Read-Host "Enter an email address or a URL for a SharePoint or OneDrive for Business site"

if ($addressOrSite.IndexOf("@") -ige 0)
{
   # List the folder Ids for the target mailbox
   $emailAddress = $addressOrSite
   # Connect to Exchange Online PowerShell
   if (!$ExoSession)
   {
       Import-Module ExchangeOnlineManagement
       Connect-ExchangeOnline -ShowBanner:$false -CommandName Get-MailboxFolderStatistics
   }
   $folderQueries = @()
   $folderStatistics = Get-MailboxFolderStatistics $emailAddress
   foreach ($folderStatistic in $folderStatistics)
   {
       $folderId = $folderStatistic.FolderId;
       $folderPath = $folderStatistic.FolderPath;
       $encoding= [System.Text.Encoding]::GetEncoding("us-ascii")
       $nibbler= $encoding.GetBytes("0123456789ABCDEF");
       $folderIdBytes = [Convert]::FromBase64String($folderId);
       $indexIdBytes = New-Object byte[] 48;
       $indexIdIdx=0;
       $folderIdBytes | select -skip 23 -First 24 | %{$indexIdBytes[$indexIdIdx++]=$nibbler[$_ -shr 4];$indexIdBytes[$indexIdIdx++]=$nibbler[$_ -band 0xF]}
       $folderQuery = "folderid:$($encoding.GetString($indexIdBytes))";
       $folderStat = New-Object PSObject
       Add-Member -InputObject $folderStat -MemberType NoteProperty -Name FolderPath -Value $folderPath
       Add-Member -InputObject $folderStat -MemberType NoteProperty -Name FolderQuery -Value $folderQuery
       $folderQueries += $folderStat
   }
   Write-Host "-----Exchange Folders-----"
   $folderQueries |ft
}

References

Use Content search for targeted collections | Microsoft Learn