I get the "Refresh token has expired" notification
The Refresh token has expired notification appears due to 90 days of inactivity between your account token in JungleMail for Office 365 and your Office 365.
Open JungleMail for Office 365 and click Create new sending account, complete the authorization process with your login and then simply cancel it. This will refresh tokens for another 90 days. If you end up not using the app again for a period of 90 days or more, you will need to repeat this procedure.