- You have mistyped your email address (i.e. your email was either sent nowhere, or elsewhere)
- Your email address can't receive email (i.e. you've exceeded your quota, your email server isn't working, your MX domain isn't configured, your spam filter requires a human to answer a challenge, etc)



Memoirs of an Email Server:
No MX for gmail.om
No MX for gnail.com
No MX for hotmail.cocm
No MX for hotmail.xom
No MX for outlook.con
No MX for optonline.ent
5.1.1 The email account that you tried to reach does not exist. Please try 5.1.1 double-checking the recipient's email address for typos or 5.1.1 unnecessary spaces. Learn more at 5.1.1 https://support.google.com/mail/?p=NoSuchUser
550 5.4.1 Recipient address rejected: Access denied [prod.protection.outlook.com]
550 5.1.1 Recipient address rejected: User does not exist.
Recipient address rejected: No need for spam. Try again later!
Not delivering to previously bounced address
Server response: 550 5.7.1 The user or domain that you are sending to (or from) has a policy that 5.7.1 prohibited the mail that you sent. Please contact your domain 5.7.1 administrator for further details. For more information, please visit 5.7.1 https://support.google.com/a/answer/172179
452 4.2.2 The email account that you tried to reach is over quota. Please direct 4.2.2 the recipient to 4.2.2 https://support.google.com/mail/?p=OverQuotaTemp