Retrieves CSV with mailbox consumption and quotas for Office 365/Exchange Online

Get-EXOMailboxSizes.ps1

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

$mailboxes = Get-Mailbox -ResultSize Unlimited
foreach ($mailbox in $mailboxes) {
    $mbSize = 0
    $mbSizeText = (Get-MailboxStatistics -Identity $mailbox.UserPrincipalName).TotalItemSize 
    if ($mbSizeText -ne "Unlimited") {
        $mbSize = ((Get-MailboxStatistics -Identity $mailbox.UserPrincipalName).TotalItemSize -replace “(.*\()|,| [a-z]*\)”, “”)
    } else { 
        $mbSize = -1
    }

    $warningQuotaSize = 0
    $warningQuotaSizeText = $mailbox.IssueWarningQuota
    if ($warningQuotaSizeText -ne "Unlimited") {    
        $warningQuotaSize = ($mailbox.IssueWarningQuota -replace “(.*\()|,| [a-z]*\)”, “”)
    } else {
        $warningQuotaSize = -1    
    }

    $prohibitSendQuota = 0 
    $prohibitSendQuotaText = $mailbox.ProhibitSendQuota
    if ($prohibitSendQuotaText -ne "Unlimited") {
        $prohibitSendQuota = ($mailbox.ProhibitSendQuota -replace “(.*\()|,| [a-z]*\)”, “”) 
    } else {
        $prohibitSendQuota = -1
    }

    $output = New-Object -TypeName PSObject
    $output | Add-Member -MemberType NoteProperty -Name UserPrincipalName -Value $mailbox.UserPrincipalName
    $output | Add-Member -MemberType NoteProperty -Name DisplayName -Value $mailbox.DisplayName
    $output | Add-Member -MemberType NoteProperty -Name IssueWarningQuotaGB -Value ([math]::Round($warningQuotaSize/1GB,2))
    $output | Add-Member -MemberType NoteProperty -Name ProhibitSendQuotaGB -Value ([math]::Round($prohibitSendQuota/1GB,2))
    $output | Add-Member -MemberType NoteProperty -Name TotalItemSizeMB -Value ([math]::Round($mbSize/1MB,2))
    $output | Add-Member -MemberType NoteProperty -Name TotalItemSizeGB -Value ([math]::Round($mbSize/1GB,2))
    $output | Add-Member -MemberType NoteProperty -Name ItemCount -Value (Get-MailboxStatistics -Identity $mailbox.UserPrincipalName).ItemCount

    $output | Export-Csv -Append -NoTypeInformation .\Office365MailboxSizes.csv
}