Before spreading these garbage emails around, I do wish people would learn to use google. Just letting it search for "mars brightest hoax" finds pages of links, near the top is
http://www.snopes.com/science/astronomy/brightmars.asp with the exact email text included. It is also possible to scroll down the page for the full explanation.
http://www.hoax-slayer.com/mars-earth-close.html is worth a look as well.
It is a fact that the planets have slightly elliptical orbits. It is also a fact that since they all circulate at differing speeds, the actual distance between them varies. The fact that the actual event referred to happened several years ago, and was nothing like the effect claimed by the perpetrator of the hoax, since it would have been widely noted at the time, should have stopped it in its tracks years ago.
Unfortunately there are many people out there who would rather believe everything they are told and pass it on rather than do a very basic check.
When I was learning about computery things, one principle that was pushed was "GIGO", or "Garbage in, Garbage out", meaning that if faulty data was provided, the answer would also be rubbish. The truth was that it really meant "Garbage in, Gospel out", because once it was processed and printed out in black and white, it was suddenly authoritative and true. The tabloids have been aware of this for a great many years, and great fortunes have been made as a result from the peddling of unsubstantiated drivel.