Empty Trash Containing Cache Files

Mailplane marks cache files as readonly which prevents them from being modified. This might prevent you from emptying the Trash if you move them manually (or via an app remover) into the Trash.

Follow these steps to empty your Trash:

1) Open Terminal app

2) Enter sudo rm -rf ~/.Trash/* and press Enter.

3) You may be asked to enter your OS X account password. Type it and press Enter.