451 errors are due to the receiving server rejecting your email. This can happen for a number of reasons but most likely is due to the recipient’s server being overloaded with messages. It can also mean that the recipient’s server has grey-listed the IP, and therefore delays the message until it can verify that the sending server is not trying to send spam. The receiving server may be offline as well.
The causes of error 451 include:
- Server limit reached
- Email rejection due to a remote anti-spam filter
- Request denied by the server
- Viral infection
If you heavily rely on email communication with your business partners and colleagues, then it is advisable to immediately resolve this issue without any delays.
Though this error is not fatal, but you should repair it right away to avoid inconvenience. SMTP error code 451 can hamper your ability to communicate via email.
Steps to Fix Outlook 451 Error-
Outlook 451 error is an error associated with processing requests procedure, you may try the following steps to fix this error.
1. If the outlook client settings are all correct, please make sure that your email supports POP mail function and confirm the relevant settings in the system is on.
2. Checks if the outlook client set up parameters is correct, especially the SMTP and POP parameters.
3. Antivirus/firewall software may block the connection of email server, please turn off the firewall/antivirus software and other security software and try again.
4. Try to a new email account if it works.