Will Schwalbe, co-author of "Send: Why People E-Mail So Badly and How to Do It Better," cautions that one can "do a lot of damage" to business and personal relationships with careless e-mail closings. Schwalbe warns against closing e-mails too frequently with words like "Best" and "Best always." But many agree that "Best" is among the best ways to close a business e-mail. Craig Brownstein, vice president of media relations at the PR firm Edelman, is one such fan of "Best" and its variants. He says he started seeing "Best" in e-mails a few years ago and has used it ever since. Others may see ending an e-mail with "Cheers" as too "mock-Brit," while "Fondly" should probably never be used to close a professional e-mail. Unless you know the person you are e-mailing very well, Schwalbe recommends against a humorous e-mail closing such as "Off like a prom dress." Brownstein, meanwhile, recently asked his research team, StrategyOne, to catalogue the most common e-mail closing lines in an online poll. The survey showed that 25 percent of participants said they close their professional e-mails with "Sincerely," while 20 percent use some variant of "Thank you" and 17 percent use no closing at all.