cant open my mail box

Try these steps in order for classic Outlook on Windows:

1. Check Outlook connection status

• Open Outlook.
• Look at the status bar at the bottom of the window.
• If it shows Disconnected, Working Offline, or Trying to connect…, Outlook is not connected to the mail server.
• Go to the Send/Receive tab on the ribbon.
• In the Preferences group, select Work Offline once to toggle back online.
• Then select Send/Receive or reopen the message and send it again.

2. Make sure the PC is online

• Open Microsoft Edge or another browser.
• Browse to http://www.microsoft.com or http://www.bing.com.
• If these sites do not open, fix the network first using the guidance in Fix network connection issues in Windows.

3. Check for large or stuck messages

• In Outlook, open the Outbox.
• Start with the oldest message.
• If any message has a large attachment (for example, over 20 MB), open it, remove the attachment, and either attach a smaller file or use a link instead.
• Try sending again. For more details, see Reduce attachment size to send large files with Outlook.

4. If Outlook will not start or keeps failing

• The Outlook profile or data files may be corrupted.
• Create a new Outlook profile:
  • Follow the steps in Create an Outlook profile.
  • Then restart Outlook and choose the new profile in the Choose Profile dialog.
• If Outlook starts normally with the new profile, the old profile was corrupted.

5. Repair Outlook and data files if needed

• Run an Office repair using the steps in Repair an Office application.
• If mail still will not open, repair Outlook data files by running the Inbox Repair Tool (scanpst.exe) as described in Repair Outlook Data Files (.pst and .ost).

6. Start Outlook in safe mode

• Press the Windows key.
• Type outlook.exe /safe and press Enter.
• If Outlook works in safe mode, an add-in is likely causing the problem. In that case, creating a new Outlook profile as above usually restores normal send/receive.

If these steps restore Outlook, sending and receiving mail should work again.

References:

• I can't send or receive messages in Outlook
• I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window”
• Can't send or receive email in Outlook.com
• Can't send or receive email in Outlook and "Metered Connection Warning" is triggered