Show mobile devices associated with each mailbox in Exchange Online

get-mobiledevicesformailboxes.ps1

# collect mailboxes that are not shared or resources
$users = Get-Mailbox | 
Where-Object {$_.IsShared -eq $False -and $_.IsResource -eq $False} |
Select-Object -ExpandProperty UserPrincipalName 

foreach ($user in $users){
    Write-Host $user -ForegroundColor green
    Get-MobileDevice -Mailbox $user |
    Select-Object -Property FriendlyName,DeviceUserAgent,DeviceAccessState, DeviceModel, Identity |
    Format-Table -AutoSize
 }
 
 # alternative one-liner; requires EXO V2
Get-EXOMailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited |
Select-Object -ExpandProperty UserPrincipalName |
ForEach-Object -Process {Get-MobileDevice -Mailbox $_ } |
Select-Object -Property FriendlyName,DeviceUserAgent,DeviceAccessState, DeviceModel, Identity |
Format-Table -AutoSize