NEF and DNG files can not be saved as.... I get the warning message that states: "None of the selected photos can be saved at high resolution."
There are no other options available. You can copy an image, but this keeps it in it's original format.
I don't think I was clear earlier with regards to how I use the 'send photo to email' function. Maybe this will make more sense; I select up to about 20 images that are in either nef or dng format. I use the send photo to email function. Then I create a folder on my desktop and take the images out of the email and place them in the new folder-hence creating full rez jpeg images. I never attempt to send that many images at full rez. I have found trying more than 20 or so images causes issues, memory or mac mail-obviously this feature wasn't intended to send 100 files at full jpeg size via email. You wind up with a 40-100mb email, or larger...
Seems that maybe under the export function you currently have to create web galleries, there could also be an 'export as' feature that would allow many of the same options as your 'send photos to email' function allows. Like custom size, full size, watermark, etc.. Really, the same options only providing you the option to have the new files sent to a folder, instead of email. I think it's mac mail that is the hang up here if you try to send say 50 images to your mail at full jpeg size.
It would be a PLEASURE to be able to point PM to a folder/selected files and have it automatically create jpegs at a desired output size and batch these into a new folder, etc... I now have to reimport images to Light Room or batch in PS. LR does the trick but it's an extra step. PM makes viewing and going through images so easy, except for taking your raw/dng files and turning them into jpegs...
Does that make sense? I use the send photos to email as a work around to create jpegs at my desire output depending on my clients needs.