I want to know too. And showing my ignorance here but...
Winlink's RMS Express will run in a Windows emulator on a Mac apparently.
But there's Dumb terminal and Outpost too, see http://www.winlink.org/ClientSoftware
Ed Kelly should know, I'll ask him, he's on the EARally atm.
Otherwise it might be simpler to buy a small netbook if you're serious about HF email.
I've not managed to get RMS Express to correctly drive the HF set (ICOM M710) through my Pactor, something that Airmail does quite happily. However I'm a Windows user, but I'd still try to find out if Airmail will run in the emulator - quick search gave http://www.sailmail.com/apple.htm