What happens when the SMTP error code 553 is encountered?

The SMTP error code 553 indicates that the recipient's email address is invalid. This means that the email server detected an issue with the specified recipient address during the sending process. The server cannot process the message because it does not recognize the recipient's address as valid, which often happens if there are typos, incorrect domain names, or if the email account does not exist.

In the context of email delivery, it's essential for the sending server to ensure that the recipient's address is formatted correctly and can be routed through the necessary domain. When faced with error code 553, the sender should check the address for accuracy, correct any mistakes, and attempt to resend the message once the validity of the recipient's email address is confirmed. This reinforces the importance of addressing quality in email communications and the need for proper validation before sending messages.