(yes, my mail server is capable to receive SSL encrypted mail, and most of providers use that capability)
Honestly you are better off doing GPG...
This. Email is inherently insecure and should be treated as such. It's not much different than sending a postcard. Adding SSL to some of the connections over which a message might travel doesn't change this. PGP (or GPG) is the email equivalent of stuffing a letter in an envelope before it goes in the mail; it keeps your message secure en route.
If the OP is really concerned about the security of his correspondence with MtGox, he should ask to exchange PGP public keys with them.