Hi Kevin,
Thanks for posting our forum.
Before going further, could you please share more more details about what you exactly mean by "It's not working fine with 10% of my user list. "?
Have you tried any troubleshooting steps which might be helpful to narrow down the issue?
Besides, to eliminate if the problem is related to any third party add-ins, you may try to start Outlook in safe mode and check if there will be any improvement.
Any findings, please post back at ease.
Best regards,
Yuki Sun
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