Hi Rene, 

   You could filter just for emails in your Documents section on your matter, then click on the first email, and hold Shift and click on the last email to select/highlight all the emails.

After all your emails are highlighted, right click over any of the highlighted emails and select Export. 

You can then save somewhere locally to upload to Dropbox.

Also as an FYI, you can also send a secure link via our Communicate app, please see our support hub article. Thanks! 

Hey there! You can hit Control A, This will allow you to select all without going one by one down the line.