Sending, receiving, and organizing email in Outlook.com
Hi, Melinda Lane
This sounds like either an account-side restriction or a synchronization problem, especially since mail stopped suddenly around a specific date. The steps below avoid repeating the storage, rules, forwarding, folder, and browser-extension checks already tried.
Here are some suggestions you can try:
Sign in at Outlook.com and send yourself a message from another email account. If it appears online but not in the Outlook app, remove the account from the app, restart the device, and add it again using the automatic Microsoft sign-in option. Do not set it up manually as POP.
If mail is also missing on Outlook.com, change your Microsoft account password, then review Recent activity at account.microsoft.com/security. Complete any security verification shown. Unusual sign-in activity can temporarily restrict an Outlook.com account even when sign-in still works.
In Outlook.com, open Settings > Mail > Sync email. If POP or IMAP is enabled but you do not knowingly use it, turn it off and test again. A connected app using POP can download or remove messages unexpectedly.
If this address receives mail from Gmail, Yahoo, or another connected account, note that Outlook.com no longer synchronizes third-party connected accounts. Add that account directly to Outlook instead.
If possible, reply with whether the test message appears on Outlook.com.