Exchange Mailbox Rules
At one of my previous Jobs, I had to write a script to help me understand rules. Well, I pulled that script out of the vault to do the same thing recently. The following script will allow you to select one user or multiple users to grab their rules. Or you can just forget the flag and get all of the users at once. The idea of the script is to get basic information from the rule, not all the information as it’s not all useful. So let’s look at the script then we will do a breakdown. Here comes Exchange Mailbox Rules through PowerShell.
The script
function Get-MailboxInboxRules {
[cmdletbinding()]
param (
[string[]]$UserPrincipalName,
[switch]$StayConnected
)
begin {
#Begining tests if the module is installed, loaded, and connected. Correcting each one at each level.
#Installs required modules
Write-Verbose "Installing required modules"
if (!(Get-InstallEdModule ExchangeOnlineManagement)) {
try {
Install-Module ExchangeOnlineManagement
}catch {
Write-Error $_
exit
}
}
Write-Verbose "Checking and importing required modules"
# Starts importanting required modules
if (!(Get-Command Connect-ExchangeOnline)) {
try {
Import-Module ExchangeOnlineManagement
} catch {
Write-Error $_
exit
}
}
#Tests if Exchange Online is connected, If not, we trigger a connection
if (!(Get-PSSession | Where-Object { $_.Name -match 'ExchangeOnline' -and $_.Availability -eq 'Available' })) {
try {
Connect-ExchangeOnline}
catch {
Write-Error $_
exit
}
}
if (!(Get-PSSession | Where-Object { $_.Name -match 'ExchangeOnline' -and $_.Availability -eq 'Available' })) {
Write-Error "Connection failed"
exit
}
}
Process {
$mailboxes = @()
if (!($PSBoundParameters.ContainsKey("UserPrincipalName"))) {
$Mailboxes = Get-mailbox
}
else {
foreach ($Username in $UserPrincipalName) {
try {
$Mailboxes += get-mailbox $username -ErrorAction SilentlyContinue
}
catch {
Write-Warning "$username has no mailbox"
}
}
}
#It has been proven to speed up the script if we drop the output into a return value
$RulesReturn = Foreach ($Mail in $Mailboxes) {
Write-Verbose "Scanning: $($Mail.UserPrincipalName)"
#We are now trying to catch the rule in question.
#if the mailbox has no rules, which will be presented as an error, then we null out the rules.
try {
$Rules = Get-InboxRule -Mailbox $Mail.Userprincipalname
}
catch {
$Rules = $null
}
#Now that the rules either have value or null, we can test.
if ($null -ne $Rules) {
#Write-Host "$($mail.userprincipalname)"
#Now we know we have rules, it's time to start working with those rules
foreach ($Rule in $Rules) {
#From my testing I discover that some rules will be null but the rule itself isn't null.
#Thus we need to test if this is the case.
if ($null -ne $rule) {
#Now we have confirmed the rule is not empty, we need to test the form
#This is because some rules are based on subjects and such and not from people.
if ($null -ne $rule.from) {
#since form is not empty we split the string and we get the from information.
$froms = $Rule.from.split('[')[0]
}
else {
#if it is, we just blank string the value.
$froms = ""
}
#Next we want the description to be on a single line. this way we can export to a csv.
if ($null -ne $rule.description) {
#This is programmed for the standard 5.1 powershell. Join-String was introduced in 6.2
#to combat this, we create a null return
#Then we split the description rule.
#Then we for each that list and push it back into the return.
$dereturn = $Null
$rule.description.split("`n") | foreach-object { $dereturn = "$dereturn $($_.trim())" }
$description = $dereturn.trim()
}
else {
$description = ""
}
#Next we create our ps object with items we need for basic level audits.
[pscustomobject]@{
Username = $Mail.Userprincipalname
Identity = $Rule.Identity
Enabled = $Rule.Enabled
Name = $Rule.Name
from = $froms
Description = $description
}
}
}
}
}
}
end {
#At the end we return
$RulesReturn
#Then we disconnect if the user didn't say stay connected.
if (!($StayConnected)) { Disconnect-ExchangeOnline -Confirm:$false }
}
}
The Breakdown
Before we begin, I want to point out, at this point, there is no graph API calls for exchange. Not yet, its promised, but as of right now, it’s not reality yet. Security is a big thing to think about with scripts like these. MFA is a big piece of security. We always want some mfa going. This is why you will not see credentials in the parameters.
Parameters
Our parameters are simple. We have a list of strings of user principal names and we have a switch to determine if we need to stay connected. If we leave the user principal name blank, then we are targeting every mailbox. It may take some time. The stay connected is designed to keep exchange connected. This way once you have the exchange mailbox rules, you can run other commands. You can also leave this blank, if you do, it disconnects from exchange. Good security thinking here.
param (
[string[]]$UserPrincipalName,
[switch]$StayConnected
)
Begin
Next is our begin. We are doing some house keeping here. First, We need to know if the exchange online management is installed. if it’s not, we then install it. Next, test if the exchange online management is imported. if not, we import the module. Finally we test if we have an exchange online connection, if not, we use connect-exchange. We use the connect-exchangeonline because it will do the MFA for us. Which is nice.
To test if the module is installed, we use the Get-InstalledModule. This command searches your modules and lets you know if it is installed. Older Powershells do not know this command. If the powershell is not elevated, then this code will error out and exits with the exit code.
Write-Verbose "Installing required modules"
if (!(Get-InstallEdModule ExchangeOnlineManagement)) {
try {
Install-Module ExchangeOnlineManagement
}catch {
Write-Error $_
exit
}
}
If we haven’t exited out yet, we then see if the module is loaded by using the get-command command. We are looking for the command Connect-ExchangeOnline. If the command exists, we will continue on, if not, we will use the import-module command and import the exchangeonlinemanagement module. Of course, if we run into an error, we exit with the error.
Write-Verbose "Checking and importing required modules"
# Starts importanting required modules
if (!(Get-Command Connect-ExchangeOnline)) {
try {
Import-Module ExchangeOnlineManagement
} catch {
Write-Error $_
exit
}
}
Finally, we are going to pull all the PowerShell Sessions currently on this computer. This is where we will gain the ability to pull Exchange Mailbox Rules. The first command is get-pssession. We search the output for a session with the name of ExchangeOnline that is available. If we don’t find one, we connect to exchange using the connect-exchangeonline. Next, if connection errors out, we present the error and disconnect. Now, if the connection is successful, we test once more for a connection. If it’s just not there, we give up and say bye.
#Tests if Exchange Online is connected, If not, we trigger a connection
if (!(Get-PSSession | Where-Object { $_.Name -match 'ExchangeOnline' -and $_.Availability -eq 'Available' })) {
try {
Connect-ExchangeOnline}
catch {
Write-Error $_
exit
}
}
if (!(Get-PSSession | Where-Object { $_.Name -match 'ExchangeOnline' -and $_.Availability -eq 'Available' })) {
Write-Error "Connection failed"
exit
}
Process – Exchange Mailbox Rules
Check Mailboxes
Now we are connected to exchange online, it’s time to start grabbing the needed information. Before we start, we need to establish an array for possible mailboxes. We will call these mailboxes to make life easy.
$mailboxes = @()
Now, whether or not the user used the “UserPrincipalName” parameter or not, we are ready. The next step is to test if we used the parameter and grab those mailboxes. We do this by using the $PSBoundParameters variable. Searching the Contains key allows you to see what parameters are being passed to the script. in our case we will be searching for the user principal name. If there is no UPN, we just grab all the mailboxes and dump it into the $mailboxes variable we made.
Now, if we did use the upn, we will loop through the UPN and grab each mailbox accordingly. if there is an issue, we let the user know that that username was an issue. This will give us the mailbox information we need. We do this separately because it causes fewer errors. Best way to describe it is using this method is the bouncer. It bounces issues out the door before we start looking at the inbox rules.
$mailboxes = @()
if (!($PSBoundParameters.ContainsKey("UserPrincipalName"))) {
$Mailboxes = Get-mailbox
}
else {
foreach ($Username in $UserPrincipalName) {
try {
$Mailboxes += get-mailbox $username -ErrorAction SilentlyContinue
}
catch {
Write-Warning "$username has no mailbox"
}
}
}
Exchange Mailbox Rules
The next step is to grab the rules themselves. We start off by making a for each loop. The loop of course is going to drop into a variable. We do this because it has been found that dropping the output of a foreach loop into a variable is a faster method than rebuilding or appending an array.
$RulesReturn = Foreach ($Mail in $Mailboxes) {}
Now, it’s time to hang onto your hats. The rules are tricky as they error out. We see errors because the end user will create a rule, and abandon it. It has nothing to do with your code. It is purely what it is.
The first thing we need to do inside our loop is grab the rules for the mailbox. The command is Get-InboxRule. We will be placing the rules into a variable called Rules. Now here is the catch. This command will produce something. So throw it in a try catch. So if it produces an error, which happens, you can set the Rules to null.
Inbox Rules
try {
$Rules = Get-InboxRule -Mailbox $Mail.Userprincipalname
} catch {
$Rules = $null
}
Next, we test if the Rules are null, if not, we start the loop. Here is another fun part… If the rule is misconfigured, it will present as null from time to time. So we need to test for the null again per rule.
if ($null -ne $Rules) {
Write-Verbose "$($mail.userprincipalname)"
foreach ($Rule in $Rules) {
if ($null -ne $rule) {}
}
}
Parsing the data
Some rules are based on subject, some rules are based on email. It’s best that we grab useful information. Things like the description, and from are presented in string format with unique structures. However, sometimes those can be null strings and that will explode the results as well. So we have to test them. First we will test the from. if the from is not null, we want to split the from, from the bracket and select the first item. However, if the from is null, we want to give the from a blank string as a psobject doesn’t like null.
if ($null -ne $rule.from) {
$froms = $Rule.from.split('[')[0]
} else {
$froms = ""
}
After the From, we need to grab the description. However, I need this description on a single line. As most people are using PowerShell 5, Join-String is not available. Which is sad. So, I built my own join-string. To do this, first create a null return. Then split the Rules description by the enter, `n. Next we do a foreach-object loop, taking that null return value and added itself to itself with a nice trim. Finally, I dropped that information into the description. If the description was null to begin with we drop a blank string into the description variable.
if ($null -ne $rule.description) {
$dereturn = $Null
$rule.description.split("`n") | foreach-object { $dereturn = "$dereturn $($_.trim())" }
$description = $dereturn.trim()
} else {
$description = ""
}
Bringing it together
Finally, we have all the information we need. It’s time to create the PS Custom Object. Here we will be presenting the username, the ID of the rule, if the rule is enabled, the from, and the description. Since we joined the strings of the description before, this output can be exported to a csv file. Remember at the beginning of the main loop, we are placing all the output of that loop into a variable called Rules Return. Well, this is what will be going into that variable.
[pscustomobject]@{
Username = $Mail.Userprincipalname
Identity = $Rule.Identity
Enabled = $Rule.Enabled
Name = $Rule.Name
from = $froms
Description = $description
}
End
Finally, we reach the end of this script. We are doing two things at the end of this script. First, we are presenting the data. Then we are testing if we need to stay connected. We present the variable Rules Return. Then we check if Stay Connected is true. If it isn’t we disconnect from exchange with a confirmation of false. If you set the flag to stay connected when you executed the code, then this part only shows the rules. No need to disconnect. I always love having this option as exchange online is a pain with multiple MFA layers.
$RulesReturn
if (!($StayConnected)) { Disconnect-ExchangeOnline -Confirm:$false }
Continue Reading:
As always, I like to present some items at the end to encourage you to continue reading.