Rules for Inbound Mail Processing (multiple addresses? searches?)
What you're requesting is possible by writing a custom extension, or possibly with CiviRules.

I managed the creation of such an extension, which is available on Github.  This extension changes the activity type of any inbound email sent to inbound+support@example.org to a different activity type.

If you're a coder, you can adapt that extension to your purpose.  If not, try using CiviRules with a trigger of "when an activity is created" and conditions that match your inbound email, and an action of "add a tag".