Saturday, May 11, 2019

Exchange Transport Rule Block Attachments While Allowing Specific Ones

In my Exchange environment we have an invoicing mailbox that auto-forwards to an external document processing email address. This mailbox can only accept PDF or TIFF attachments, since that's what the doc processing service will accept. So, I needed a way to only allow those two attachment types, while blocking all others.

Articles on the Web are spotty on how to accomplish this...most are all or nothing. MS TechNet has an article on blocking all attachments, but we need to allow the ones mentioned above to come through. In this post, I'll expand on that.

We'll be using the EAC (Exchange Admin Center) to create our Transport Rule (aka Mail Flow Rules) since it's a little bit easier to see all of our options.

In the EAC, navigate to Mail Flow > Rules.
Click the "+" and select "Create a new rule...":

EAC Create New Rule

In the rule creator, give it a name.

Under "*Apply this rule if..." select "the recipient is..." and then search for and select your recipient(s).

Click the "more options" link and then click "add condition".

Drop-down to "any attachment" then mouse over to "is greater than or equal to..."

Input "1" in the field - for 1KB.

**Note** The EAC will only accept 1KB as the lowest value, which will block all attachments in my experience. If you need to go lower, like 0KB, you'll need to use the Shell to set it later.

Under "*Do the following..." drop-down to "Reject the message with the explanation..." and enter your outgoing bounce reason. In my case I specify that only PDF and TIFF are allowed.

Under "Except if..." drop-down to "Any attachment's file extension matches..." and enter "tiff" and "pdf".

**Note** Don't enter a dot in front of the file extensions, as it will throw an error; only enter the extension name.

Set your priority and leave "enforced" selected.

Click "Save"

The results should look like so:

EAC Attachment Rule Settings

Basically, what we did is block all attachments, but since we set an exception, we allowed those two specific ones through.
This might seem counterintuitive at first, but think if you did it the other way around and had to manually block every file type...that would take forever!

**Note** In the above example I set the rule for one mailbox, but if you need to allow only these certain attachments to all mailboxes, under "Apply this rule if..." you would choose "the recipient is... located inside the organization". You can also set it to "a member of this group" if you have groups set up for different settings.

Now, test your rule by sending a blocked attachment like a JPEG, to the mailbox and then send an allowed attachment like a PDF.

The blocked attachment should generate a 5.7.1 reply like so:

Delivery has failed to these recipients or groups:

invoices@exchangeitup.com (invoices@exchangeitup.com)

This message was rejected because only PDF or TIFF attachment types are allowed.

Your message wasn't delivered because the email admin for the organization 'exchangeitup.com' created an email rule restriction. Please contact the email admin for that organization and ask them to remove or update the rule restriction.
For more information about this error, see DSN code 5.7.1 in Exchange Online - Office 365.

As you can see, the sender will get the 571 bounce, and it includes my custom outgoing message under the recipient email address: "This message was rejected because only PDF or TIFF attachment types are allowed."

Happy attachment blocking!

Saturday, May 4, 2019

Outlook Teams Add-in Overrides Skype Meeting Add-In

My company uses Teams for meetings internally, but many of our clients use SFB on-premises, so we need to be able to schedule meetings in both modalities depending on the attendees.

The problem is: once Teams is installed, the Teams Outlook add-in takes precedence over the SFB add-in - the SFB add-in actually gets disabled.

If you enable the add-in from within Outlook > Options > Add-ins > COM Add-ins, it will revert back to "unloaded" when you next log on...maybe this Microsoft's way of forcing everyone to Teams, I dunno, but they need to fix it!

Here's what I'm talking about: in Outlook, only the Teams add-in will be shown when setting a new meeting: 

Outlook Teams Only

To fix this, you need to hack the registry to force Outlook to show both Teams and SFB.

To manually set it, navigate to:


The LoadBehavior key will most likely be set to "0" which is Off.

LyncAddin LoadBehavior Off

We need to set the LoadBehavior key value to "3" which is Load At Start:

LyncAddin LoadBehavior On
If you don't have the key present (sometimes it won't be there), or don't want the hassle of setting it, you can grab the reg file from my Google Drive. Installing this will create the key if it's missing, or set it to "Load At Start" if it's in there already.
You can also use PowerShell to set the key, by running the following cmdlet in an Elevated PS session:
Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\Outlook\Addins\UCAddin.LyncAddin.1" -Name loadbehavior -Value 3
There's no need to restart the machine with either the reg change or the Shell method, the changes will automatically take effect.
Now, when creating a new meeting, both add-ins will be shown:
Outlook SFB And Teams

You can push out the reg file in a GPO if you have a lot of machines that are affected - in my case it was only a few of us.

Saturday, March 23, 2019

Office 365 Create Remote PowerShell Shortcut

In a previous post, I showed how to create a Remote PowerShell shortcut for Exchange on-premises, to save you from having to type in the remote session every time you connect.

Since I've been doing more work in O365, I decided to do the same for that; especially because Office 365 has many more connections you have to run, such as Exchange, Skype For Business/Teams, Azure AD, and Security Center.

This PS shortcut will install and import those sessions and get you signed in all in one shot.

First, set your PowerShell execution policy - I use Unrestricted but you can use RemoteSigned:

Open PowerShell as admin, and run:

Set-ExecutionPolicy Unrestricted

Next, enable PS remoting by running:


Then, install the required modules:

For MSOL, run:

Install-Module MSOnline

**Note** We're using MSOL because it's more comprehensive than AzureAD

**Note** Running the above cmdlet should install the latest version straight from the PowerShell gallery. If it doesn't, browse here and grab it:


Next, download the Skype for Business Online Connector module from here:


**Note** As of this writing, the SFB Online Connector will manage Teams as well.

Next, copy the following block and paste it into Notepad:

$credential = Get-Credential
$exchangeSession = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri
https://outlook.office365.com/powershell-liveid/ -Credential $credential -Authentication "Basic" -AllowRedirection
Import-PSSession $exchangeSession -DisableNameChecking
$SccSession = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri
https://ps.compliance.protection.outlook.com/powershell-liveid/ -Credential $credential -Authentication "Basic" -AllowRedirection
Import-PSSession $SccSession -Prefix cc
Connect-MsolService -Credential $credential
Import-Module SkypeOnlineConnector
$sfboSession = New-CsOnlineSession -Credential $credential
Import-PSSession $sfboSession

**Note** I left out the SharePoint Online connection, because in order to run it without errors you either need to set your local DNS to Google's, or use the web login and that's a pain - plus I don't manage SharePoint, so......

**Note** The Exchange Online and Security Center won't work if you run MFA. For that, you need to install the EXOPS modules, which can't be run in a single window.

Save it as a .ps1 with a name like O365-Remote.ps1 to somewhere like C:\Scripts

Next, create a PowerShell shortcut anywhere, like on your Desktop:

Right-click the Desktop > New > Shortcut

New Shortcut

In the location field, enter:


PowerShell Shortcut

Click Next

Give it a name like O365RemotePS and click Finish.

O365 Remote Shortcut

Right-click the new O365RemotePS shortcut, and go to Properties.

In the Target field, add the following to the end of the line:

-NoExit -File "C:\Scripts\O365-Remote.ps1"

It will look like so:

C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe -NoExit -File "C:\Scripts\365-Remote.ps1"

Click OK.

Run your new shortcut as admin, and you'll get a creds prompt for your Office 365 organization.

**Note** Enter creds in the username@orgname.com format.

Once it starts the remote session, you'll be able to run your O365 cmdlets.

Remote MSOL

Remote CSUser
Remote Mailbox

Tuesday, February 19, 2019

Exchange 554 5.7.105 sender's email address is on SenderFilterConfig list

One of my users submitted a ticket that "an important client was getting blocked by our spam filter". Checking the filter, all messages from that sender were clean and not being blocked at all. After further digging i.e. the user finally gave me the NDR that the external sender was getting:

host [] said: 554 5.7.105 SenderFilterAgent; Sender denied as sender's email address is on SenderFilterConfig list

**Note** In the above bounce message, the "host IP address" refers to my Edge server.

In message tracking, it shows the same bounce message; you can view that by running the following in the EMS (Exchange Management Shell):

Get-MessageTrackingLog -Sender sender@externaldomain.com -Start "2/18/19 8AM" -End "2/18/19 5PM" | fl *RecipientStatus*

RecipientStatus : {[{LED=554 5.7.105 SenderFilterAgent; Sender denied as sender's email address is on SenderFilterConfig list};{MSG=};{FQDN=};{IP=};{LRT=}]}

This could be one of two things:

The sender or external domain is on the SenderFilterConfig BlockedSenders/BlockedDomains on the Exchange Edge or Mailbox Server(s)


The sender/domain is listed in the User's MailboxJunkEmailConfiguration blocked senders list in Outlook.

I do run an Edge server, but I don't have entries in the Sender Filter Config (because I run a 3rd party spam filter) as seen here:

Get-SenderFilterConfig | fl *block*

BlockedSenders               : {}
BlockedDomains               : {}
BlockedDomainsAndSubdomains  : {}
BlankSenderBlockingEnabled   : False
RecipientBlockedSenderAction : Reject

Upon checking the User's Junk mail config, bingo! She had hundreds of senders in there; this particular sender being one of them.

**Note** The User also had the sender in the TrustedSendersAndDomain list, but the block list takes precedence over allowed.

To view the list, run the following in the EMS:


The above cmdlet will allow you view the entire list because if it's large, PowerShell will truncate it.

Then, run:

Get-MailboxJunkEmailConfiguration -Identity "user mailbox" | fl *block*

**Note** Change "user mailbox" to the user you're dealing with.

You can then right-click the Shell title bar and Edit > Find to search for the suspect sender.

Now, let's remove that sender from the blocked sender list:

Set-MailboxJunkEmailConfiguration -BlockedSendersAndDomains @{remove="sender@domain.com"}

**Note** Replace "sender@domain.com" with the actual email address of the sender.

One thing I noticed: the removal of the sender from the blocked list didn't take effect immediately. In fact it didn't do anything for the hour I waited. 
The background operation that happens is: even though the blocklist is client-specific, it pushes that setting up to the Exchange servers, and if you run an Edge, it will need to EdgeSync over.

In order for the sender to be cleared from the blocked list, I had to disable/re-enable the SenderConfig on the Edge.

To turn off the Sender Filter Config, run:

Set-SenderFilterConfig -Enabled $false

Then, run:

Set-SenderFilterConfig -Enabled $true

After that, the messages starting being delivered successfully! Now, tell your user they don't need to add every single sender in world to the blocklist, your spam filter can handle the heavy lifting ;)

Saturday, December 29, 2018

Exchange 2016 Create Remote PowerShell Shortcut

A growing trend for organizations is to lock down direct remote access to servers, requiring the need for Remote PowerShell Sessions to manage things like Exchange. The problem is, it's a nuisance to create a remote session every time you need to connect to Exchange.

To save time (and my sanity) I decided to create a shortcut that will start the remote session automatically when you run it.

Copy the following information into Notepad:

$UserCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri http://mail.exchangeitup.com/PowerShell/ -Authentication Kerberos -Credential $UserCredential
Import-PSSession $Session -DisableNameChecking

**Note** Change -ConnectionURI to match your Exchange namespace or a server name (if you don't publish PowerShell).

Save it as a .ps1 with a name like Exchange-RemotePS.ps1 to somewhere like C:\Scripts

Next, create a PowerShell shortcut anywhere, like on your Desktop:

Right-click the Desktop > New > Shortcut

New Shortcut
In the location field, enter:
PowerShell Shortcut
Click Next
Give it a name like ExchangeRemotePS and click Finish.
ExchangeRemotePS Shortcut

Right-click the new ExchangeRemotePS shortcut, and go to Properties.
In the Target field, add the following to the end of the line:
-NoExit -File "C:\Scripts\Exchange-RemotePS.ps1"
It will look like so:
C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe -NoExit -File "C:\Scripts\Exchange-RemotePS.ps1"
Shortcut Target
Click OK.
Run your new shortcut, and you'll get a creds prompt for your Exchange organization.
Once it starts the remote session, you'll be able to run your Exchange cmdlets.
Remote PowerShell Session
Now, you can use that new shortcut instead of tiring out your fingers before even getting into Exchange!

Sunday, December 2, 2018

Exchange 2016 Planning Diagram: Hybrid

If you follow my blog, you know that I like to use Visio to draw pretty pictures to use when planning out Messaging Environments. Examples can be found here, here and here. The diagrams really come in handy when presenting a build to a new client, or to your higher-ups so they can see what the finished setup will look like.

I just happen to be planning out an Exchange 2016 Hybrid scenario, which will use the current on-premises Exchange environment and expand it out to Office 365. What a great chance to create a new diagram!

Feel free to grab the Visio diagram further down in the post and edit it to match your environment, in order to save time in creating one yourself.

Exchange 2016 Hybrid Planning Overview

In my example below, we're starting with a 3-node Exchange 2016 DAG with the accepted domain of "domain.com" and "mail.domain.com" as the namespace.

We have a two-arm Load Balancer (one NIC or "arm" in the DMZ, and one in the Internal LAN) which will server up mail.domain.com for our users that have mailboxes homed on-prem.

An on-premises Skype For Business Front End (SFB1.domain.com), with Unified Messaging going to the on-prem Exchange servers.

We're going to expand the on-prem Exchange out into Office 365, creating a Hybrid Environment.

This will require adding:

An Azure AD Connect Server for DirSync (AAD.domain.com)

An ADFS Server for authentication (ADFS.domain.com)

And installing the Hybrid Server on Exchange (hybrid.domain.com)

**Note** You'll want to edit the generic names of the domain to match your environment.

As you can see in the diagram, all the new servers are added, with the connection flow to/from Exchange and O365.

Exchange 2016 Hybrid Overview

To edit the diagram to fit your organization, you'll need to download the Exchange/Office 365 Visio stencils from Microsoft, so the shapes will render correctly.

Once you have those downloaded, move them to C:\Users\Your_User\Documents\My Shapes

Then, hop over to my Google Drive and grab the Exchange Hybrid Overview.vsdx

Happy diagramming :)

Sunday, October 28, 2018

SFB Invoke Failback Error: Cannot Open Service

We recently updated our Skype For Business environment to CU7 (July 2018 Update). Since we have such a large SFB organization (20+ servers) I and another admin tag-teamed the install so it wouldn't be an all day affair.
When it came time to run the Invoke-CSComputerFailback cmdlet, the other admin was hit with the following error in the Skype For Business Management Shell:

WARNING: Invoke-CSComputerFailback failed.
WARNING: Detailed results can be found at


Invoke-CSComputerFailback : Command execution failed: Cannot open RTCXMPPTGW service on computer "SFB-FE1.exchitup.com".
At line:1 char:1
+ Invoke-CSComputerFailback -Computer SFB-FE1.exchitup.com
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 + CatagoryInfo  : InvalidOperation: <:> [Invoke-CSComputerFailback], InvalidOperationException
 + FullyQualifiedErrorId : ProcessingFailed,Microsft.Rtc.Management.HADR.ComputerFailover.

If you browse to the location of the logfile in the error, the XML and HTML reports show the following, respectively:


<?xml version="1.0" encoding="UTF-8"?>
-<CsMgmtLog Name="Invoke-CsComputerFailBack">
<Info Time="2018-10-27 17:31:33Z" Title="Connection">Data Source=SFB-FE2.exchitup.com;Failover Partner=SFB-FE3.exchitup.com;Initial Catalog=xds;Integrated Security=True;Application Name=Microsoft.Rtc.Management</Info>
<Info Time="2018-10-27 17:31:37Z" Title="Host">SFB-FE1.exchitup.com</Info>
<Info Time="2018-10-27 17:31:37Z">Enabling services at SFB-FE1.exchitup.com...</Info>
<Error Time="2018-10-27 17:31:37Z" Title="Error">An error occurred: "System.InvalidOperationException" "Cannot open RTCXMPPTGW service on computer 'SFB-FE1.exchitup.com'."</Error>

-<Exception Time="2018-10-27 17:31:37Z" Message="Cannot open RTCXMPPTGW service on computer 'SFB-FE1.exchitup.com'." Type="InvalidOperationException">
<StackTrace Time="2018-10-27 17:31:37Z"> at System.ServiceProcess.ServiceController.GetServiceHandle(Int32 desiredAccess) at System.ServiceProcess.ServiceController.get_ServiceHandle() at Microsoft.Rtc.Management.Deployment.Core.NTService.set_Mode(StartMode value) at Microsoft.Rtc.Management.HADR.ComputerFailover.InvokeComputerFailBackCmdlet.EnableServices(DeploymentContext context) at Microsoft.Rtc.Management.HADR.ComputerFailover.InvokeComputerFailBackCmdlet.InternalProcessRecord() at Microsoft.Rtc.Management.Deployment.DeploymentCmdlet.CmdletProcessRecord()</StackTrace>

-<Exception Time="2018-10-27 17:31:37Z" Message="Access is denied" Type="Win32Exception">
<StackTrace Time="2018-10-27 17:31:37Z"/>


SFB HTML Error Log

The Fix:

Run the Skype For Business Management Shell as administrator, then  try the cmdlet again.

**Note** I always set the shortcut for the Shell to Run as Admin, so I don't have to do that every time. I wish it just would out of the box since I am, you know, an admin :)

Right-click shortcut, Properties > Advanced button > Run As Administrator > Ok

Now your cmdlets should run successfully and you can finish your updates!

Saturday, October 6, 2018

Exchange 2016 Publishing REST/OData For API With Kemp Load Balancer

Our company is designing an app for users to have an all-in-one-do-everything portal that will incorporate a mail client that connects to our on-prem Exchange. The app utilizes the Outlook Mail REST API to grab messages from the user's mailbox.

**Note** Office365 supports REST by default; it wasn't until Exchange 2016 CU3 that it was available for on-prem (go figure).

You can find the details here:


If you're running on-prem, you should be patched up way beyond CU3, right?

The issue is: REST API is enabled on Exchange 2016 CU3+ but if you run a load balancer, like Kemp's super-awesome Load Master, the API won't be published out of the box.

By default, the Kemp Exchange templates don't enable Exchange API to be published. As a workaround, you can enable the "default" content rule on your SubVSs, but some IT security departments won't like that, because it's a blanket rule.

What we'll do instead, is create a Custom Content Rule, and apply it to our OWA SubVSs ('Sub-Virtual Services), which will allow the API to be published.

Create The Rule:

In your Load Master WUI, go to Rules & Checking > Content Rules > Create New Rule:

Kemp Add New Rule 1

Give it a name like "REST_API"

Rule type: leave as default (Content Matching)

Match type: leave as default (Regular Expression)

Match string: type in the following:


Tick Ignore Case

Click Create Rule:

Kemp Add New Rule 2

Your new rule will be listed:

Kemp Rule Created

Adding The New Rule:

Next, we'll add our new content rule to our OWA SubVSs

Navigate to Virtual Services > View/Modify Services

Click Modify next to your Internal Service:

Kemp Modify VSs 1

**Note** You can modify your external service if you want; it would just depend on your security requirements. For instance, our IT Security Department doesn't understand Exchange and therefore won't allow me to publish OWA externally, so I can only publish the API internally as well.

Expand SubVSs, and click the Rules button next to OWA:

Kemp Modify VSs 2

In the drop-down, select our new "API_REST" rule and click Add:

Kemp Add Rule 1
Kemp Add Rule 2
You'll now see the API_REST rule listed for the OWA rule set:
Kemp Rule Added to VSs
Testing The New Rule:
In a web browser navigate to your Exchange namespace with the API URL at the end, like so:
You will be presented with a Save/Open JSON prompt:
Mailbox json prompt
Open in Notepad, and you'll see your messages in your mailbox:
Mailbox API Messages Content
Now your on-premises Exchange API REST/OData is published, and the app (or whatever needs that service) can hit it!

Saturday, September 1, 2018

Exchange 2016 Recover Deleted Items To Original Folder Script

I recently had a huge issue in my Exchange environment where a retention policy went haywire and wiped mail from all User Mailboxes in the organization.

Backstory: We migrated from Notes last year, and the legal department wanted to institute retention policies moving to Exchange. I (stupidly) let another admin tag those migrated messages with an EWS script (which BTW, I said from the beginning isn't the best way to do it, and of course no one listens me) but they did it anyway. Fast-forward a year later, and the tag from that script got removed because it was named "test" and Exchange never threw a warning saying that it was applied to any mailboxes, which un-tagged all mailboxes, which deleted years worth of mail. Yippee.

So I desperately needed a way to get those messages back; preferably to their original folders, in bulk, without manually going to each mailbox to recover items from the Recoverable Items folder (aka the dumpster).

Exchange on-prem doesn't have this capability (it should, Microsoft are you listening?) so I scoured the webs and finally found a solution! An EWS script that moves items from the Recoverable Items folder back to the original folder they were deleted from.

***Starting with Exchange 2016 CU1, items are stamped with a LastActiveParentEntryID (LAPEID) attribute, but it couldn't be utilized until CU6; and it can only be accessed from OWA, not from Outlook, not from PowerShell.

Credit goes to Scott at flobee.net, who wrote an AMAZING script that ports the Restore-RecoverableItems from O365 to on-prem (again, this should be available in the first place, not everyone wants to, or even can move to O365, Microsoft).

The original script can be found here

The problem is: it did not work all the way; running with more than one parameter, caused the script to result in no output.

What I mean is: if I ran the script with the "-FilterStartTime" and "-FilterEndTime" or "-FilterStartTime" and "-FilterItemType" it wouldn't do anything...I could only use one of those parameters.

So, I edited the script to use AQS (Advanced Query Syntax) and hardcoded a date range so it will run successfully.

Saving The Script:

Grab the RecoverableItemsAQS.psm1 from my Google Drive here.

**Note** It's a .psm1 file. That's a PowerShell module that you need to import into your PowerShell session, which I'll show you later.

Open the script in Notepad and search for AQS and change the date range in the following block; you'll need to do this in both the Get-MailboxRecoverableItems and Restore-RecoverableItems sections:

  $AQS = 'received:4/22/2015..6/7/2017'

Edit the date range to fit your needs.

Also, change the page size in both sections to 1000; the default is 50.

Search for:

$pageSize = 50

You will also need the EWS API 2.2 installed on the machine where you'll be running the script from. Best is to install this on a non-Exchange server as it can cause some serious performance issues on Exchange - see my previous post for those issues.

Running The Script:

After you've made the above changes, save the script somewhere like C:\Scripts

There are two functions of the script: Get Recoverable Items, and Restore Recoverable Items.

**Note** You cannot pipe the Get function into the Recover Function, it is only for reporting.

Get Recoverable Items:

**We're going to be using Impersonation to run against mailboxes. This is easier and more secure than setting Full Access on a bunch of mailboxes. You'll need to pass the credentials into the script for the account that has impersonate rights to run both Get and Recover.

To set up impersonation follow this TechNet guide.

In the EMS, run:

Import-Module "C:\Scripts\RecoverableItemsAQS.psm1"

Then to get a list of items in the dumpster output to a txt file, run:

Get-MailboxRecoverableItems -Identity staceybranham@exchangeitup.com -UseImpersonation -Credential (Get-Credential) | Out-File c:\temp\staceydeletions.txt

**Note** The -UseImpersonation and -Credential (Get-Credential) parameters are for your impersonation account you set up earlier. You'll be prompted with a Widows cred prompt.

Restore Recoverable Items For A Single User:

In the EMS, run:

Import-Module "C:\Scripts\RecoverableItemsAQS.psm1"

Next run the following to recover on a single mailbox:

Restore-MailboxRecoverableItems -Identity staceybranham@exchangeitup.com -UseImpersonation  -Credential (Get-Credential)

Restore Recoverable Items In Bulk:

To run the recovery on a multiple mailboxes, we'll pipe in a CSV list of email addresses, and run the script against each of those.

Create your CSV where the heading is SMTPAddress, then each user's email address on each row like so:


Save it as MailboxImport.csv somewhere like C:\Scripts.

Next in the EMS, run:

$cred = get-credential

**Note** These creds will be the account you're using that has Impersonation Rights

Then, run:

$mailboxes = Import-CSV "C:\Script\MailboxImport.csv"; $mailboxes | foreach {Restore-MailboxRecoverableItems -Identity $_.SMTPAddress -UseImpersonation -Credential $cred}

Use caution when running the script on a bunch of mailboxes at one time, because it generates transaction logs, just as regular mail-flow does.

Test with groups of mailboxes to see how big your log volumes are growing before you run the script on a large batch. In my experience, recovering ~9GB of deleted items generated 1 to 1.5GB of logs.

My advice is to split up your Import CSVs into 10-20 mailboxes per day (or per backup cycle) so the logs will truncate in between runs -or- stagger the groups of mailboxes which are homed on different DB's...say 2 or 3 mailboxes per DB in each list.