According to other reports online, Microsoft is experiencing issues across their email products (Outlook, MSN, Hotmail, Office365, etc.) Specifically, these issues are impacting many third-party email apps (not just Edison Mail/OnMail.) Please see this page for more details: https://downdetector.com/status/outlook/
One potential (but not guaranteed) workaround that has been successful for some of our users is deleting the account from our app's settings, and then re-adding it, however instead of using the Outlook/MSN/Hotmail/Office365 account option at setup, choose Microsoft Exchange and use your credentials.
We will continue monitoring this situation with our users and our own test accounts, and we remain hopeful that Microsoft will address this on their end ASAP. If you use other, non-Microsoft accounts in our app, they shouldn't be impacted by this issue, however we strongly advise accessing your Microsoft accounts on the web via a browser in the meantime, especially if timely delivery of your incoming/outgoing messages for that account is necessary – at the very least until this issue is resolved. Our apologies for the inconvenience this is causing!