Sometimes, a PEN may just be temporarily unavailable. Other times, the PEN may simply not exist any longer. In either case, it is not possible for the client to synchronize email2 messages with the PEN. If this is the first time that you have received a message from this PEN, you will be asked to activate with it. This may also happen if your local information has been manually edited or removed.
In both cases, (whether the server is down, or if the PEN just doesn't exist anymore), the activation procedure will fail. If the activation fails, you will be offered the chance to block this PEN, which will mark it as disabled. Disabled PENs can always be re-enabled later using the email2 options, so if you believe that this is only a temporary problem with the PEN, you can use this option to avoid seeing the error message more than once.