Outlook Not Sending or Receiving: What's Actually Wrong
Can't sign in at all? Different issue — see my Outlook login post. This one's for when you're in, but mail just isn't moving the way it should.
The one thing to check before anything else
Look at the bottom status bar. If it says "Working Offline," stop right there — nothing past this point matters until that's fixed, because Outlook literally isn't talking to the server. Send/Receive tab → Work Offline to toggle it back.
Stuck sending
Open the Outbox before you do anything else. In my experience it's almost always a single stuck message — usually one with a big attachment — jamming up everything queued behind it. Deal with just that one message and the rest of the queue tends to clear itself.
Not receiving anything new
Force a manual check first: Send/Receive tab → Send/Receive All Folders. If you get an actual error, read it carefully — the exact wording tells you precisely what failed instead of leaving you to guess. No error but also no new mail? Check whether the account's sync settings quietly reverted after a recent update, which happens more than people expect.
Fine for a while, then it just stops
This pattern — working, then silently stuck — usually points to a corrupted local data file rather than a settings problem. Repairing the account (Control Panel → Mail → Email Accounts → Repair) fixes this far more often than a full profile rebuild ever needs to.
Fine on the website, broken in the app
Check Outlook.com directly. Mail's there but not in desktop Outlook? The problem is entirely local — nothing wrong with your account at all.