Microsoft Outlook supports crossing through selected lines of text using the strike-through button found under the Format Text tab. Use double strike-through formatting using the Font dialog box.
Single Line
Step 1

Highlight a word or line of text while composing a message.
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Tip
When forwarding a message, click the Pop Out button above the message to open it in a new window.
Step 2

Open the Format Text tab, and then click the abc (strikethrough) icon in the Font group.
Tip
Alternately, press the A, O and 4 keys in sequence to apply strike-through formatting on highlighted words and lines of text.
Double Line
Step 1

Open the Format Text tab and then click the small arrow-shaped icon in the Font group.
Tip
The Font dialog box also opens when you click the small arrow-shaped icon in the Plain Text group under the Message tab.
Step 2

Check the box next to Double strikethrough and then click OK.