Curious, what is the purpose? I get 10+ hours of bat life and don't run out of memory. Is it really worth all the worry, time and effort? Maybe it is just curious.
If you have Backgrounder installed, you should be able to use the overrides in the latest updates to disable the native functionality of the mail app. You can set it to close on exit and stay closed.
If you have Backgrounder installed, you should be able to use the overrides in the latest updates to disable the native functionality of the mail app. You can set it to close on exit and stay closed.