Comment by dingaling
10 years ago
Yes, even if you blacklist mail explicitly outbound to Gmail a huge number of companies still use it under the covers through Google Apps. I suppose you could blackhole their MX through local DNS.
Other than that the only real protection is encryption but aside from my pension provider and a former ISP I have not encountered companies that advertise a PGP key.
Dreamhost and Facebook both let you receive PGP-encrypted emails. (And it seems "all" major news sites now have PGP-keys listed somewhere …)