Do grab attention with your subject line. Examples: “Apology for the late reply” or “Sorry about what I said in the meeting.” By letting them know your intentions up front, it’s more likely they’ll read your e-mail right away.
Do set up a time to talk for lengthier apologies. If the other person is upset, he or she may not appreciate an out-of-the-blue phone call. Use e-mail to broach the topic and set up a time to call to apologize.
Do make amends quickly. People often stall before sending an apology because they try to phrase it perfectly or avoid apologizing in the first place. Send it sooner rather than later, so the recipient spends less time feeling burned.
Do ask yourself before you send your “I’m sorry” message: Is e-mail really the best way to apologize? People don’t always take e-mail apologies seriously. The very fact that you apologized by e-mail can add insult to injury. If you don’t receive a reply to your e-mail apology, it’s generally a good indication that it fell short.
Don’t “cc” without permission. Copying others on your apology will make it appear less sincere. Once you’ve apologized to the person you’ve wronged, you can contact anyone else who needs to know.
For more tips, check out Send by David Shipley and Will Schwalbe.