When you reply to a message in a shared mailbox, the other ones (who also has access to that mailbox) can see that you have replied, but not what you have replied. The answer itself ends up in your own private sent folder.
To collect your answers you can create a folder and a filter.
- Create a new folder that you save in the level below the shared folder.
- Go to the Preferences tab > Filters.
- Click the Outgoing Message filter> New filter.
- Give the filter a suitable name and the conditions as in the picture below.
- Keep the box in front of the Do not process more filter selected > OK.