First off, I'd use sRGB for images that are mailed.
Second: I'm not sure I get what you are saying:
If you export using sRGB, AdobeRGB 1998 or ProPhotoRGB (not a good idea for 8bpc images), then they all look off in mail? By the same amount?
Mail is color managed, so should handle all images (with embedded ICC profile!) correct. Since LR embeds the icc profile, this should work.
I gave it a quick try, exported an image in ProPhotoRGB (to make sure that it would be obvious if mail weren't color managed), and opened that in Mail.
Looks identical (except the output sharpening done; LR 2.0 Beta)
.
If it works different for you, then something is wrong with your monitor profile perhaps.
I have once had a monitor profile that was recognised by PS, but not by the OS; it was located in the wrong folder. If you make a screenshot (Cmd+Shift+3), and open that in PS, what profile does it have? Should be the same as your monitor profile. If not, you have the same problem I had.