1. In Outlook Web Application, click on +New
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2. Click on the 3 elipses
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3. Click on Show From
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4. When you can see your name, Right Click
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5. Choose Remove
6. The From area will be Empty
7. Start typing the name of the person you want to send as (you must already have the permissions otherwise, it will look like it works but you will get a failure message)
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8. Click on the name you want to use.
9. Now complete your message as normal