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You can change the font and its color, size, and style—such as bold or italic for all messages you send. For example, you can change the message text to blue or use the font Arial instead of the default Calibri.
If you want to change font styles for messages you reply to or forward, under Replying or forwarding messages, click Font.
If the font you choose isn't installed on the recipient's computer, the recipient's mail program substitutes an available font.
In Outlook 2013, the default font used when you create, reply to, or forward an email message is 11-point Calibri.
Hope this helps.