RPost U.S. Inc.'s e-mail service, which might be considered the registered mail of the Internet, has a cool new feature. SideNote, says Zafar Khan, CEO of the Los Angeles-based company, lets you provide "context" to recipients of an e-mail message who are being "carbon copied" (cc) or "blind carbon copied" (bcc).

For those unfamiliar with the world of paper letters and memos, Khan explains that in the old days, missive writers would scribble notes explaining to people why they were getting cc'd or bcc'd on a given message. But in the e-mail era, that flexibility vanished. He says people often call or send additional e-mails to people being cc'd or bcc'd to give the context for the e-mail. With SideNote, RPost users simply click on a button in their mail clients and write a bright-yellow note for each cc and bcc recipient. Recipients need not be users of RPost and can even get SideNotes on their BlackBerries or iPhones. SideNote comes free with the standard RPost service. RPost has plug-ins for Outlook, Notes and GroupWise mail clients. Pricing starts at $59 per 100 registered e-mails.