Determine when a user can start sending email again after hitting the 10,000 Recipient Rate Limit in Exchange Online

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.