Join us at FabCon Atlanta from March 16 - 20, 2026, for the ultimate Fabric, Power BI, AI and SQL community-led event. Save $200 with code FABCOMM.
Register now!Calling all Data Engineers! Fabric Data Engineer (Exam DP-700) live sessions are back! Starting October 16th. Sign up.
Hi,
I am trying to connect to an Outlook mailbox and performance is great but as soon as I try to expand a list column that contains the category of each emails, the performance drops to a point where its no longer usuable. I tried deleting all the columns and limit myself to 5 columns but expanding that category column is problematic. I absolutely need the content of that column for my reporting and to filter out a lot of emails from my report.
Any help would be greatly appreciated.
Hi @Whoule ,
Before expanding the list columns, make sure that only the necessary columns and rows are imported. Use Power Query to filter the dataset to what you actually need for your analysis. You can select Transform Data when connecting to your mailbox and use the Choose Columns feature to limit the data to only those columns you need.
When expanding the list column, try to do this after you have filtered the data to reduce the volume of data that needs to be processed. Consider writing a custom M query to expand only the necessary elements of the list column, which can be more efficient than using the automatic expand feature.
Best Regards,
Dino Tao
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.
@Anonymous Hi, so basically, I am using that list column to filter out all emails with a completed tag on them but in order to filter these out I need to expand that column to get its value. Would you happen to have a good link to share on custom M query for specific expend values?
Join the Fabric FabCon Global Hackathon—running virtually through Nov 3. Open to all skill levels. $10,000 in prizes!
Check out the October 2025 Power BI update to learn about new features.