Hi,
Do you have your three email account set up in the same mail profile in Outlook?
Do you have your email accounts configured on any mobile devices? Such as your cellphone? If so, please try temporarily disabling the synchronization on these devices and then check if this issue continues.
In addition, please also try starting Outlook in safe mode (outlook /safe) and then check if this issue continues. This will help determine if this issue was caused due to problematic add-ins.
Regards,
Steve Fan
TechNet Community Support
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