Boards can also be added from message attachments:
In the above example, the selected message header is highlighted in
blue. Below is the associated message for this header.
Beneath that is the attachment for this message. In this
case the attachment are the keys for a board. In this example we
already have the software board. Lets pretend we don't and want to
add it's key. We simply select the attachment by left-clicking it,
then press the icon highlighted in yellow. If you already have
the key for this board in your keypool folder/directory a window will
open asking if you wish to replace the one you have with the new one.
Your answer depends upon whether you are updating to a new key or
not. If not, no need to add the key again.
As with most things, there is an alternative to clicking the icon,
and that is after selecting the board attachment, right-click on it and
you will be presented with a small menu window from which you can select
various choices: