Hi,
Which version of Outlook are you using?
What kind of drop-down menu do you mean? Do you mean the Context Menu when we right-clicking on an email or a specific drop-down menu? Would you please provide a screenshot to clarify the issue? You can share the screenshot to us via sending it to GBSD TN Office Information Collection ibsofc@microsoft.com. (The email subject should be the thread link.)
In addition, we can try to open Outlook in safe mode to see if this issue continues. Press Windows key + R to open the Run command, type outlook /safe and press Enter. If the problem would be gone in safe mode, we can go to (In Outlook 2010 or Outlook 2013) File > Options > Add-ins and disable suspicious add-in to resolve the issue.
Regards,
Steve Fan
TechNet Community Support