you are using Apple's Mail program as your email client, here's how
you can remove the emails
in your trash. Go ahead and open up Mail, the stamp icon on your dock.
When you are on your inbox on the left column all of your emails will
be displayed on the right side of the window. When you select an email
and delete it, that email will be sent to the trash where it will remain.
In order to delete the emails in the trash, first click on the Trash
Icon in the left column. Now you will see that all of the trash emails
are displayed on the right of the window. You will also notice that the
delete button is grayed out. So to delete the trash emails, simply click
on one of them and then you have the option to click the delete button.
Once you click the delete button the email is gone forever. Go ahead
and click the delete button and you will see that your email is gone.
If you want to delete them all at once, use the keyboard shortcut for
select all, Apple and the "A" key. This selects all of your
trash email. Now click the delete button and all of your trash emails
will be gone!