Get-MailboxSize

Function Connect-EXOnline {
    param (
        [string]$Credential
    )

    $credentials = Get-Credential -Credential $Credential
    Write-Output "Getting the Exchange Online cmdlets"

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

}

Function disconnect-EXOnline {
    $session = Get-PSSession
    foreach ($id in $session) {
        if ($id.ConfigurationName -eq 'Microsoft.Exchange') {
            Remove-PSSession $session
        }
    }
}

function get-MailboxSize {
    param (
        [string]$UserMailbox
    )
    $CheckConnection = Get-PSSession
    cls
    if($null -eq $CheckConnection){
        Connect-EXOnline
        cls
    } else {
        if ($CheckConnection.ConfigurationName -ne "Microsoft.Exchange"){
        Connect-EXOnline
        cls
        }
    }

    $totalItemSize = Get-MailboxStatistics $UserMailbox | Select-Object TotalItemSize
    $totalItemSize = ($totalItemSize.TotalItemSize.value).tostring()
    $totalItemSize = $totalItemSize.trimend(" bytes)")
    $totalItemSize = $totalItemSize.Split("(")
    [string]$totalItemSize = $totalItemSize[1].Trim()
    $totalItemSize = $totalItemSize.Replace(',', '')
    [uint64]$MailboxSize = $totalItemSize / 1MB

    Write-Host $UserMailbox
    Write-host "Mailbox Size (MB):"

    $TotalItemSize = $null
    return $MailboxSize
}


#UserMailbox is the Mailbox you want to find the size of.
get-MailboxSize -UserMailbox '<Enter Email Address>'