If you USE ALL CAPS in your email, you will immediately make yourself look like a newbie. For those of us who spend a lot of time hanging out in cyberspace, using all capital letters in a message is akin to shouting. For those new to the Internet, this restriction might seem silly. However, using all caps WILL adversely alter how people perceive you online.
Capital letters are best left for their intended usage and, sparingly, to emphasize a particular word or phrase.
If you wish to communicate effectively via email, the importance of Email Etiquette should not be underestimated.