Windows Mail + Encryption

[species8350]

Hi,

I would like to send encrypted mail and am trying to set up a Digital
ID.

On using the Wizard, I am having difficulty at the stage where I am
asked to specify a file to import. Can someone advise.

I also note that I have a number of certificates in Intermediate
Certificate Authorities, and Trusted Root ..., nothing in Personal,
and Other People. Can someone also explain their significance?

Thanks

Ps. Why does the mail programme only encrypt to 168 bits?