Scenario: While attempting to run Exchange Online PowerShell commands against a large group of mailboxes and/or returning large datasets, you may run into mico delays or other errors once you breach any number of throttles that Microsoft Online imposes against your PowerShell session. Although throttles protect Microsoft Online for good reason, your still left with the question “WHY ME?” and how do we get around these strict restrictions.

Solutions: There’s a few ways to execute commands in Exchange Online PowerShell, but each have their own advantages and disadvantages. Below are a few examples with running the command: get-mobiledevicestastics which is naturally heavy in processing and subject to breaching throttles.


Standard Command – This may work if you only have a small number of mailboxes in your environment. Its quick, but also dangerous.
$AllMailboxes.alias | Get-mobiledevicestatistics -mailbox $_



ForEach with a Mini-Sleep – This command will help with some of the throttling, its not difficult to execute by implementing a 2-command loop and will help with the recharge rate for how many commands you are allowed to execute within a time period.

$AllMailboxes.alias | %{ Get-mobiledevicestatistics -mailbox $_; Start-Sleep -milliseconds 500}
-or-
$AllMailboxes.alias | ForEach { Get-mobiledevicestatistics -mailbox $_; Start-Sleep -milliseconds 500}


Invoke-Command to help with Large Data Return – Invoke with Select-Object forces the O365 servers run the command and limits the data returned. This takes your local client out of the loop helping to ease local client throttling. HOWEVER invoke command doesn’t allow complex PowerShell commands either.

Invoke-Command -session (Get-Pssession) -scriptblock {Get-mobiledevicestatistics -mailbox $_ | select-object identity, Device*,LastSuccessSync}
-or-
Invoke-Command -session (Get-Pssession) -scriptblock {Get-Mailbox -resultsize unlimited | select-object -property Displayname,Identity,PrimarySMTPAddress}


Microsoft Module: RobustCloudCommand – Microsoft created a module that can be used, originally it used to be a script. The module is designed to stay under the throttling limitations imposed by Microsoft. The module keeps an eye on the amount of commands issued, the amount of time or data collected, throttling errors, and so on. The module will tear down and rebuild the PowerShell session when needed and pickup where the script left off. AND one of the coolest things is that it supports Modern Auth and will renew your OAUTH tokens automatically. Let those big scripts fly! The only issue I see is that its limited in complex PowerShell commands. However if you want to run a single command, such as adding a BlockEverything Authentication Policy for every single one my theoretical 400K users, the workhorse below will do the trick

Install-Module -Name RobustCloudCommand #https://www.powershellgallery.com/packages/RobustCloudCommand

$users = Import-csv C:\temp\AllMailboxes.csv

Start-RobustCloudCommand -recipients $Users -logfile C:\temp\out.log -ScriptBlock {Get-user $input.userprincipalname -AuthenticationPolicy BlockEverything}

Scenario: Recently we had a user who hit the 10K Recipient Rate Limit in a 24 hour period within Exchange Online. This user was performing two types of emailing from their ExOnline mailbox: 1. Sending mass mailings from their Mailbox using their from address and 2. Sending mass mailings from their Mailbox and setting another From Address (Delegated Send-as Permissions for a Service Account). Both types of sending impacted the recipient rate limit for the persons mailbox.

BTW – Do not mass mail directly to recipients from an ExOnline mailbox. Instead use distribution groups or other third party mailing systems to send mass communications.

Scriptlet: Here is a scriptlet to help determine when the user should be able to send from their mailbox again. The results provide hourly recipient counts for the sender which may help in determine the timeframe when a user should no longer be impacted by the 24 hour period:

Edit the Variables in the scriptlet and paste it into Exchange Online PowerShell.

#Edit these variables
$sender= “SteveTheMassMailer@domain.com”
$start = “1/7/2021”
$end = “1/9/2021”
$pageSize = 1000
$P = 1
$messages = $null
$report = @()
$totalRecipients = 0

#Loop for All Messages
do
{
Write-Host “Message Trace – Page $P…”
$temp_Messages = Get-MessageTrace -senderaddress $sender -startdate $start -enddate $end -PageSize $pagesize -Page $P
$P++
$Messages += $temp_Messages
}until ($temp_Messages -eq $null)

#Display messages or Message Count
#$Messages
$Messages.count

#Build the Loop Parameters
$Loop_start = get-date($messages | Sort Received | Select -expandproperty Received -First 1) -format “MM/dd/yyyy HH:00:00”
$Loop_end = get-date($messages | Sort Received | Select -expandproperty Received -last 1) -format “MM/dd/yyyy HH:00:00”
$1Hour_end = get-date($Loop_start)
$1Hour_end = $1Hour_end.AddHours(1)
$1Hour_end = get-date($1Hour_end) -format “MM/dd/yyyy HH:00:00”


#Now Loop It!
“Starting Loop for $sender”
Do{
“Checking $Loop_Start and $1Hour_end”
$RecipientCount = $messages | Where {($_.Received -gt $loop_start) -and ($_.Received -lt $1hour_end)} | Select RecipientAddress
$totalrecipients = $totalRecipients + $recipientCount.count
$recipientCount = $RecipientCount.count

#Report it
$obj = New-Object PSObject
$obj | Add-Member NoteProperty -Name StartTime -Value $Loop_Start
$obj | Add-Member NoteProperty -Name EndTime -Value $1hour_End
$obj | Add-Member NoteProperty -Name RecipientCount -Value $RecipientCount
$Report += $obj

#New Variables
$Loop_Start = $1hour_end
$1Hour_end = get-date($Loop_start)
$1Hour_end = $1Hour_end.AddHours(1)
$1Hour_end = get-date($1Hour_end) -format “MM/dd/yyyy HH:00:00”
}While( (get-date($Loop_start)) -lt (Get-date($Loop_End)))

#Summary
$report
“#Summary######################################################”
“-Results are reported in GMT”
“- Total Recipient Count for $Sender between $start – $end : $TotalRecipients”




Microsoft Example of the 24 hour Recipient Rate Limit:
After the recipient rate limit is reached, messages can’t be sent from the mailbox until the number of recipients that were sent messages in the past 24 hours drops below the limit. For example, a user sends an email message to 5000 recipients at 09:00 AM, then sends another message to 2500 recipients at 10:00 AM, and then sends another message to 2500 recipients at 11:00 AM, hitting the limit of 10,000 messages. The user won’t be able to send messages again until 09:00 AM the next day.