When the same thing happens online through a dating site, the interaction is much less multi-faceted. However dating site members still make decisions based on less obvious aspects than just what the person writes in their e-mail. As a Queensland University of Technology study discovered, aspects such as grammar and spelling can be influential.
It seems that some people can be turned off if the person they're communicating with is a sloppy writer, or one who goes overboard with the exclamation marks. So it's probably a good idea to take a bit of care when replying to e-mails on these sites.