How do I remove old matched emails from Activity History?

Please note that if emails have matched into Activity History, then you are using Standard MatchMyEmail.  The data is part of your Salesforce data and you can use native mass delete tools within Salesforce to manage.

To delete older Activity records (older than specific date – use Due Date field of task for filtering)

1. 1. In Salesforce, go to  Setup.  In the left sidebar, at the top in Quick Find type Mass Delete and click on the option below Mass Delete Records.
2. In the list, click on Mass Delete Activities
3. Read through the first two points to be sure you understand and have created backups as desired.  Read the information that is displayed on the screen that explains what will be deleted and recommends making a backup
4. In the table of filters, you would want to choose the following
   1. Subject –  Starts with  –  and type in Email:
   2. Status  –  equals  – and type in Completed
   3. Due Date   –  less than   –  your date of choice
   4. 
5. Click the Search Button.
6. Select the messages desired and click Delete button.  These would move into Recycle Bin and you can Restore at later date.   You can also check  “Permanently delete the selected records.” before Delete, to totally delete the records from Salesforce.