This article explains how to add strikethrough text in macOS Mail using the format bar. This information applies to macOS Big Sur (11) through macOS Sierra (10.12).
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When you send a new email or forward or reply to a received email, you can add a strikethrough to text in macOS Mail by selecting the text and then clicking the Strikethrough Formatting button. Adding a strikethrough to email text doesn’t delete it, but it does indicate to the recipient(s) that you’ve changed your mind about that content or that the information is no longer valid.
The strikethrough button appears in the Mail formatting bar above the body of new emails and email replies. You can cross out words, letters, or entire paragraphs using the strikethrough button in the formatting bar.
Open a new email, forward, or reply screen in the macOS Mail app. Click the A button in the upper-right corner of the message window to display the formatting bar, if it isn't already visible. The formatting bar is centered above the message and contains controls for font, size, text color, alignment, and other aspects of text formatting.
