Support FAQ - Why do activities get added when users reply to notifications?
Why does this happen, and who is to blame?
Microsoft of course!
First review the configuration of the exchange connector to understand how this could happen:
What this particular setting is doing is on update of an existing workitem (when subject = [ID]) add the response to the action log AND apply what values\actvities are set on the particular template, which in this case is the Default Service Request:
To be fair there is no other template that could be used so to have a value here the only option was Default Service Request.
To fix this issue simply create a new template that contains no values or activities, give it a pretty name such as "Blank SR" or "Exchange Connector SR Template" and update your connector: