Lion Mail easily bypasses encryption

If for some reason Mail is not closed when Lion closes down, such as during a crash, then when Lion restarts it automatically restarts Mail. Mail then decides I have no mail and sets about recovering it all from my Mobileme account.
If I close Mail during this process then restart it, Espionage intervenes and asks for a password before Mail loads the encrypted Mail and Mail Downloads folders.
The problems are: 1. I can't seem to stop Mail downloading my mail if it starts automatically. 2. There seems to be now a second Mail folder somewhere with a large amount of unencrypted mail downloaded into it. 3. How secure is the entire encryption process if it's only necessary to open Mail in this manner to gain access to all my Mail?
I'd like to stop the automatic downloads, clear the stored second Mail folders, and prevent anyone from being able to ever get my mail by such a simple method as otherwise the encryption provides very little protection.
Any helpful advice would be appreciated.
Thanks for your time and expertise.
If I close Mail during this process then restart it, Espionage intervenes and asks for a password before Mail loads the encrypted Mail and Mail Downloads folders.
The problems are: 1. I can't seem to stop Mail downloading my mail if it starts automatically. 2. There seems to be now a second Mail folder somewhere with a large amount of unencrypted mail downloaded into it. 3. How secure is the entire encryption process if it's only necessary to open Mail in this manner to gain access to all my Mail?
I'd like to stop the automatic downloads, clear the stored second Mail folders, and prevent anyone from being able to ever get my mail by such a simple method as otherwise the encryption provides very little protection.
Any helpful advice would be appreciated.
Thanks for your time and expertise.