Phone calls, in person meetings. The contracts are usually privileged, so those can be shuffled around in email (the contents are still discoverable, but things like pricing are usually redacted.)

At least two of the very largest deals in one company I worked for were never discussed in email, and all parties met in person, and paper (!) notes were taken. It was only once all the essential details were agreed to (Memorandum of Understanding) and hammered out, that the final details were locked down by attorneys via standard electronic means.

Note, this is particularly important, if you are discussing things that might be coming close to (if not actually crossing) the lines of legality.

See: http://community.seattletimes.nwsource.com/archive/?date=199... for details of one such meeting.

Encrypted email (PGP) has been really easy to set up and use for about a decade now, particularly Enigmail.