To ensure all your activities show up under the Activity History (as opposed to Open Activities) make sure you have a "Completed" values in the Task Status list and that it's a "Closed" state.
Here is how to check it:
- In SFDC, go to Setup > App Setup > Customize > Activities > Task Field. Click on Status
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- In the Task Status Picklist Values list, check if you have a "Completed" value. If you do have it, skip to step 5.
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- You need to create the "Completed" value. Click on the New button
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- Type in Completed and click on Save
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- Click the Edit link next to the Completed value
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- Check the box next to Closed and click on Save.
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Once the steps above are completed, you should now Completed in the list with "Closed" checked like this:
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