If you’re like me and need to report on inactive accounts so that they can be disabled, this PowerShell script might help you out:
Get Office365 inactive accounts:

$UserCredential = Get-Credential
Import-Module MsOnline
Connect-MsolService -Credential $UserCredential
$exchangeSession = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri “https://outlook.office365.com/powershell-liveid/” -Credential $Usercredential -Authentication “Basic” -AllowRedirection
Import-PSSession $exchangeSession -DisableNameChecking
Get-Mailbox -ResultSize Unlimited | Get-MailboxStatistics | where {$_.LastLogonTime -lt ((get-date).AddDays(-90))} |
Select Name, Alias, UserPrincipalName, ForwardingSMTPAddress, ForwardingAddress, DeliverToMailboxAndForward, displayname, lastlogontime,  |
Export-csv c:\temp\O365InactiveUsers03082016.csv -NoTypeInformation