Hi AleB
I'm AnnaThomas and I'd happily help you with your question. In this Forum, we are Microsoft consumers just like yourself.
Sorry for the trouble this might have caused. You can try changing the default apps by file type from the settings
Right-click on the start menu
click on apps and features
default apps
Scroll down and choose default apps by file type, then choose Outlook(new)
If you still cannot open the file type, you can switch back to Old mail. On Outlook click on the switch New Outlook.
Outlook new is still been improved on and as such might not be able to open the file type in question
I hope this helps ;-), let me know if this is contrary to what you need, I would still be helpful to answer more of your questions.
Best Regards,
AnnaThomas
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