23 April 2021

Cannot open the Outlook window. Invalid XML

Microsoft Outlook has got to be one of the most common business applications that just about everyone uses. So when it fails to open, it can feel like the start of a bad day. One error message that I have encountered a few times now is the “Invalid XML” message when trying to launch Outlook. The most common reason for this error is that the XML file that contains the settings for Outlook’s navigation pane has become corrupted. The navigation pane is the one that is on the left side of Outlook and lets you change between your mailbox, folders, calendar, contacts, tasks, etc.

So how do we fix the error? The first thing to try is to simply reset the navigation pane.

  1. Hit ‘Windows+R‘ on your keyboard to open the ‘Run‘ window.
  2. Type in the following command: Outlook.exe /resetnavpane
  3. Hit the ‘OK‘ button.
  4. Then re-launch Outlook to verify that everything is working.

If the above action did not resolve your Outlook issue, then the next course of action would be to delete the actual XML file and force Outlook to generate a new/fresh file the next time it opens. Here’s how we can do that.

  1. Hit ‘Windows+R‘ on your keyboard to open the ‘Run‘ window.
  2. Type in the following command: %AppData%\Microsoft\Outlook
  3. Hit the ‘OK‘ button.
  4. It will open ‘File Explorer’ and take you to the directory that the XML file resides in. Look for a file named ‘Outlook.xml
  5. Delete the XML file.
  6. Then re-launch Outlook to check that it is working now.

That is how to fix the Outlook ‘Invalid XML’ error. I hope one of these methods worked for you so you can get back to your emails.

24 December 2019

Office 365 – Winmail.dat

After changing over from on-prem Exchange to O365, I had one user where the recipients of their emails would receive any attachment that was sent as the “dreaded” winmail.dat file instead of the .pdf or whatever file the user was actually sending. It was intermittent however, in that some users would get the actual file and some (all external) would get the winmail.dat file.

First thing that I did was check that user was sending their mail as HTML, and not Rich-Text. After changing that value, I check back a week or so later and the user was still experiencing the issue, so it was time to dig a little deeper. After some searching online I was able to find that this was not an uncommon issue.

The issue happens because the receiver’s email client can not interpret the email message that was sent from Outlook in the Rich-Text format. When using Outlook to end an email using the Rich-Text format, a plain text copy of the email is also sent along with an attachment named winmail.dat. This ‘winmail.dat’ attachment is what contains all of the formatting, elements, and other data specific to Rich-Text email messages. This method of sending the email message is called “Transport Neutral Encapsulation Format” or “TNEF” for short.

Unfortunately, many non-Microsoft email programs can not properly open message that are received in TNEF. To fix this, we can use PowerShell to force Exchange Online to convert Rich-text messages to HTML before it sends it off. You can use the commands shown below to set the ‘RemoteDomain’ property “TNEFEnabled” to false on the Default policy.

1) Connect to Exchange Online via Powershell.

2) Get your Default RemoteDomain policy:
Get-RemoteDomain | fl *

3) Set the TNEFEnabled property:
Set-RemoteDomain Default -TNEFenabled $false
Re-run step 2 and you should see that “TNEFEnabled” is set to “False”.

Just in case… Here is how to change it back to a NULL value to undo your change in step 3, and let the Outlook client again decide how it wants to send the message.

4) Set the TNEFEnabled property back to NULL:
Set-RemoteDomain Default -TNEFenabled $nul

13 November 2019

Outlook O365 – minimized window issue

Had an issue today with a user using O365 Outlook. Whenever they tried to open a message in a new window, it open it as a minimized window, showing only dots, then the minimize/full screen/close window icons.

I could use the “windows key + [ARROW]” buttons to move and essentially resize the window. But after closing and re-opening the message, it was the minimized window as before. I tried resizing it and holding “SHIFT” when closing the window, but that didn’t work either. Everything i tried basically wouldn’t persist. Every time i closed the window and reopened it, it would be that same minimized window.

What did end up working for me was to close Outlook, and make a registry edit. This is the registry key I deleted:


After that, opening messages in a new window worked as expected again.