What is the difference between a COM Add-In and an Outlook/Office Add-In?

COM Add-In vs Outlook Add-In

COM Add-InOutlook Add-In
Specific to Windows computers
Work on any web-based Outlook platform
Supplemental program that runs at startup of OutlookConsists of a manifest that describes how the add-in integrates into Outlook, as well as JavaScript/HTML code.
Are downloaded .dll or .exe files that are installed on your PCDoes not have any code that is installed on your device

Outlook add-ins are different from COM or VSTO add-ins, which are older integrations specific to Outlook running on Windows.

PoliteMail does not use any VSTO add-ins.