If it hasn’t happened to you already, it will. You set out to respond to a group email with a message meant for only the sender but hit “reply all” instead of just “reply.” You may realize your error immediately. You may discover it later, when angry and/or perplexed responses start to roll in. Either way it’s too late.
You might be tempted to blame “computer malfunction” or even sabotage but few people will believe you, so you’re better off owning up to the mistake and asking for forgiveness. Keep it short, humble and sincere. If what you wrote was harmless or merely annoying, try a lighthearted “My bad” or “Well, that was awkward.”
On the other hand, if your message was hurtful or seriously rude, then a heartfelt apology to the injured party is in order. Do it sooner rather than later. Apologies are most effective when delivered before the situation has had a chance to fester.
Next, since you want this to never happen again, consider some these preventive measures:
Wait for it. Switch to an email program that can be set to wait 60 seconds after you hit “send,” giving you time to think twice and abort the whole thing. Many email programs also offer an “undo send” feature that deletes messages from recipients’ inboxes. This only helps if they haven’t yet opened the message, however, and some work only if you’re using the same server.
Hide it. You might also try moving the “reply all” button to a less convenient spot (i.e., not right next to the “reply” button) or setting up the program so a simple “reply” is the default choice.
Forward it. A low-tech solution that works with all email programs is to make a habit of always clicking on “forward” instead of “reply.” The address box will thus stay empty until you physically enter in the correct address. This method requires a few additional steps but you will never again suffer the agonies of an unintended “reply all.”
A final note: For those times when you’re on the receiving end of someone else’s botched “reply all,” please do not answer with yet another “reply all.” This only amplifies the problem. Notify the sender individually and then, because it happens to all of us, let it drop.