Hi,
Does this issue happen when attaching a certain file or a random file to Outlook emails?
Are you attaching a file from local drive or a network drive?
We may first try to start Outlook in safe mode and then see whether this issue continues. To do this, press Win key + R to open the Run command, type
outlook /safe and press Enter. This could help determine whether a problematic add-in is the culprit.
Besides, do you have any mapped drives? These mapped drives could slow outlook down as it connects to each drive before attaching the file.
Regards,
Steve Fan
Please remember to mark the replies as an answers if they help and
unmark them if they provide no help.
If you have feedback for TechNet Subscriber Support, contact
tnmff@microsoft.com.