RGB* means that the document colorspace is different from your working colorspace. This means the image had an embedded profile tag, but that you have Photoshop set not to convert images to the working profile upon opening them.
The * is just a reminder of this.
And for when you encounter it.....RGB# means the image is untagged, i.e., Photoshop doesn't know what profile to use because the image was saved without profile information, and you have told Photoshop to not color-manage these images.
As for sending an RGB* via email...I don't see a problem. I have just tested this and attached an RGB* file to an outlook express email and sent it to myself.
You will not see the image in the body of the email when sending, but upon opening, it shows (as well as being an attachment).
I did this by using the right click option of Send To > Mail recipient and also by dragging the file into the body of the email. Worked both ways.
If you wish to remove the * you need to assign the profile to the image that matches the working space profile.
To do this for one image at a time, go to Edit > Assign Profile, and choose the profile from the drop down (third option) to match the one in place in the second line, the Working one.
I always have PS convert files automatically to my working space choice of Adobe RGB.
This is because it has a larger gamut (wider range of colours) and I process my images with printing in mind.
A consequence of this can be slightly washed out images when viewed on the web as all browsers will show images in the sRGB colourspace profile (except for Safari on the Mac).
This is because the browser cannot convert all the available colours and some are, for want of an easier explanation, discarded.
Personally, this doesn't bother me and you can always convert to sRGB for posting to the web once you have finished editing if you would prefer.
To change how PS manages the profiles the same way that I have set, go to Edit > Colour Settings and set as the following......
Hope this helps :)