I'm not receiving or able to send emails in outlook

For Outlook.com or Outlook on the web, use these checks first:

1. If the account password was changed recently, update the sign-in in Outlook:
   • Select the icon next to the email account name.
   • In the pop-up, select Continue.
   • Follow the prompts and enter the new password.
   • If prompted to create an app password, get it from the email provider and paste it when Outlook asks for the account password.
2. If messages are stuck because of large attachments:
   • Open Outbox.
   • Start with the oldest stuck message.
   • If it has an attachment larger than 20 MB, remove it and attach a smaller file or a link instead.
   • Try sending again.
3. If using Outlook on the web and mail can be received but not sent:
   • Go to Settings > Mail > Sync email and verify the sending address under From.
   • Go to Settings > Mail > Compose and reply and reset the default From address.
   • Clear the browser cache or try another browser.
   • Sign out, then sign back in.
4. If using the Outlook app for iOS and setup or sync is the issue:
   • Open an in-app Outlook support ticket and use Contact Support to chat with agents in the app.
5. If the issue continues in classic Outlook for Windows:
   • Check the bottom status bar. If it shows Disconnected, Working Offline, or Trying to connect…, go to Send/Receive > Work Offline to switch back online, then try Send/Receive again.
   • Confirm internet access by opening a browser and testing http://www.microsoft.com or http://www.bing.com.
   • Use the Microsoft Support and Recovery Assistant automatic check for Outlook connectivity issues.
6. If self-service steps do not resolve it, contact support:
   • For classic Outlook, start with the Classic Outlook troubleshooters page. If that does not work, use contact support.
   • For Outlook on the web or account-related receiving issues after a security event, contacting Microsoft Support is the appropriate next step.

References:

• I can't send or receive messages in Outlook
• I can not send emails but I receive them - Microsoft Q&A
• Set up the Outlook app for iOS
• Help Identify My Issue with Sending/Receiving Email in Outlook (Automatic Checks)
• Issues sending and receiving email
• I can't receive emails. - Microsoft Q&A