Sending, receiving, and organizing email in Outlook.com
Hello,
What is the exact error message the sender receives when they try to email your address?
You can try sending a test email from one of your accounts to the affected email address. If you receive any bounce-back error message, share the complete error message here.
Meanwhile, please check your e-mail forwarding rules.
If your incoming emails are forwarded to another address, click 'Do not forward' and save the settings.
And check whether you have enough storage to send or receive emails.
In addition to this,
Make sure you have protected your Microsoft account with a Strong password and enabled two-factor authentication for added security.
So, even if someone knows your password, they will not be able to sign in without the additional layer or security. That is the verification code from your recovery contact methods.