Configuring preferences and options in Outlook.com
Hi Tina,
Welcome to Microsoft Community!
Thank you for bringing up this issue to our attention. We understand that fonts keep on changing when you are composing emails. Let me assist you with your concern. Microsoft is aware that some users where having issue of font keep on changing when composing an email. We apologize for the inconvenience this matter has caused you. Please be informed that our Product Group is working on a fix. There is no ETA for this.
If you have other concerns, please do not hesitate to contact us back.
Regards!