Using Powershell To Whitelist Your Emails In M365 - KAMIND IT

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Blog Using Powershell to Whitelist Your Emails in M365 July 3, 2020 kamind Blog

Another way you can add domains to a Whitelist in M365 is by using a script known as “PowerShell”. To do this, follow these steps:

1. Make use of this specific script:

Param(
[Parameter(Mandatory=$True,Position=1)]
[string]$ruleName,
[Parameter(Mandatory=$True)]
[string]$domainListFilePath
)
#Read the contents of the text file into an array
$safeDomainList = Get-Content $domainListFilePath
#Create a new array and remove all text for each line up to and including the @ symbol, also remove whitespace
$newSafeDomainList = @()
$newSafeDomainList += foreach ($domain in $safeDomainList)
{
$tmpdomain = $domain -replace “.*@”
$tmpdomain.trim()
}
#If the rule already exists update the existing allowed sender domains, else create a new rule.
if (Get-TransportRule $ruleName -EA SilentlyContinue)
{
“Updating existing rule…”
$safeDomainList = Get-TransportRule $ruleName |select -ExpandProperty SenderDomainIs
$completeList = $safeDomainList + $newSafeDomainList
$completeList = $completeList | select -uniq | sort
set-TransportRule $ruleName -SenderDomainIs $completeList
}
else
{
“Creating new rule…”
$newSafeDomainList = $newSafeDomainList | sort
New-TransportRule $ruleName -SenderDomainIs $newSafeDomainList -SetSCL “-1”
}

2. Using the “Notepad” feature in Word, type in your domains to be listed as follows:

nicedomain.com trusteddomain.com tachytelic.net [email protected]

3. Connect to the Exchange Online Portal using PowerShell. For instructions on how to do that, click on the below link:

https://docs.microsoft.com/en-us/powershell/exchange/connect-to-exchange-online-powershell?redirectedfrom=MSDN&view=exchange-ps

Run the script illustrated in Step #1 with these kinds of parameters:

.\Add365SafeDomains.ps1 -ruleName “Safe Domain List” -domainListFilePath “c:\domainlist.txt”

It is important to the note the following:

*If you are already using an existing rule, any duplicate domains are automatically purged;

*The domain list is thus sorted into an alphabetical order for easier reading in M365;

*If you a create a rule name that does not already exist, a new rule will thus be automatically created.

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