Currently, the Windows build is very buggy and is not officially support.
Use at your own risk.
If you want to install an old version of Bitmask, you can browse all releases.
To get encrypted email to work, you have two options:
Manual email client configuration:
localhost:1984
localhost:2013
You should also disable any local caching in your email client, if applicable. All the data stored by Bitmask is kept on disk in an encrypted format, but your mail client might cache your email in clear text, so it is good to disable caching if you can. Also, all your Bitmask email is sync'ed locally anyway, so there is no benefit to local caching.