We've all been there: you blind copy (or bcc) someone into an email chain, they reply all - and your cover is blown.
Well now, Debrett's, the publisher of a centuries-old guide to British upper-class decorum, has deemed the practice of bcc-ing "deceptive".
Debrett's, which was founded in 1769 and describes itself as "a source on British social skills, etiquette and style", has published an updated guide to modern manners.
Perhaps unsurprisingly, the issues of concern have changed over the past few hundred years, with this year's guide including sections on the use of mobile phones, MP3 players and "social netiquette".
But one of the most commonly asked questions involves the dreaded bcc - which the publisher says needs to be "used with discernment; It is deceptive to the primary recipient."
Instead of bcc-ing a third party into an email, Debrett's says the email should be forwarded on to this party after it's been sent. The only time a bcc is appropriate, according to the publisher, is when sending a confidential email where recipients need to remain anonymous. Then, the sender should bcc all recipients while addressing the email to themselves.
But not everyone is convinced. Lucy Kellaway, associate editor and management columnist of the Financial Times, describes Debrett's alternative as "rotten"
"Of course, Debrett's is right that the bcc is underhand. But then offices are always going to be places where some of what happens is a bit underhand as information does not flow freely," she wrote in a column for the FT.
Other workplace advice from the latest Debrett's Guide include: "never repeatedly check your phone during a meeting" and "never discuss salary with your colleagues".
People are also advised that "illicit material spreads like wildfire so talk with caution within the office walls".
- By CNBC's Katrina Bishop