$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $M365Cred -Authentication Basic -AllowRedirection

Import-PSSession $Session -DisableNameChecking

## Get All Devices and Mailboxes metadata, store in memory/variable
## Torey should verify I'm pulling ActiveSync devices correctly:
#$AllDevices = Get-MobileDevice  # All Devices
$AllDevices = Get-MobileDevice -ActiveSync # Only ActiveSync I hope
$AllMailboxes = Get-Mailbox -ResultSize Unlimited

# Loop through each device, get a part of its identity, and match that identity part with a mailbox, 2400 devices took about 20 minutes to run
$result = @()
$count = 0
ForEach ($Device in $AllDevices) {
    $count++
    write-warning ($count.tostring() + '/' + $AllDevices.Count)
    #clear loop variables
    $Mailbox = $null
    $DeviceDisplayName = $null
    $ADUser = $null

    $DeviceDisplayName = $Device.Identity.split('\')[0]
    $Mailbox = $AllMailboxes | Where-Object DisplayName -eq $DeviceDisplayName
    If($Mailbox){
        $ADUser = Get-ADUser -Identity $Mailbox.PrimarySmtpAddress.split('@')[0] -Properties CanonicalName
    }

    # create custom object to show only information we want
    $obj = [PSCustomObject]@{
        DeviceDisplayName  = $DeviceDisplayName;
        DeviceAccessState  = $Device.DeviceAccessState;
        MailboxName        = If($Mailbox){$Mailbox.Name};
        PrimarySmtpAddress = If($Mailbox){$Mailbox.PrimarySmtpAddress};
        Agency             = If($Mailbox){$ADuser.CanonicalName.split('/')[1]};
        DeviceFriendlyName = $Device.FriendlyName;
        DeviceUserAgent    = $Device.DeviceUserAgent;
    }

    # store new object in array
    $result += $obj
}

Write-Output $result