Ooh, I know this one! I think. Doesn't Apple Mail have this built in? I go to Keychain Access, choose the option to generate a key. Two clicks. Head to Mail, encryption options are there. Now, to import his key. Do some googling on that.
Wait, what? Apple Mail supports S/MIME, not GPG. Competing standards strike again.
If the other person has S/MIME, Apple Mail does have a very easy experience. I can't speak for the merits of either security-wise.
Also, I think this is the sort of thing Keybase is good for. There's a level of indirection pasting into Keybase, but it's pretty easy to set up and (for non-Snowden levels of paranoia) makes it very easy to start sending encrypted mail to somebody else. The new Keybase chat is also an option.
Wait, what? Apple Mail supports S/MIME, not GPG. Competing standards strike again.
If the other person has S/MIME, Apple Mail does have a very easy experience. I can't speak for the merits of either security-wise.
Also, I think this is the sort of thing Keybase is good for. There's a level of indirection pasting into Keybase, but it's pretty easy to set up and (for non-Snowden levels of paranoia) makes it very easy to start sending encrypted mail to somebody else. The new Keybase chat is also an option.