503 5.5.1 rcpt mail failure

A classic error message!

The error message "503 5.5.1 rcpt mail failure" is a SMTP error code that indicates a problem with the recipient address. Here's a breakdown of the code:

• 503: This is the SMTP error code, which indicates that the command was not accepted.
• 5.5.1: This is the specific error code, which indicates that the recipient address is invalid or cannot be found.
• rcpt: This refers to the RCPT TO command, which is used to specify the recipient address of an email message.
• mail failure: This is a descriptive text that indicates that the email message failed to be delivered due to the invalid recipient address.

Common causes of this error include:

1. Invalid recipient address: The recipient address is misspelled, does not exist, or is not a valid email address.
2. Domain not found: The domain name of the recipient's email address cannot be resolved.
3. Mail server configuration issue: There may be a problem with the mail server's configuration, such as a misconfigured DNS record or a firewall blocking the email traffic.
4. Email client or server issue: The email client or server may be experiencing a temporary issue, such as a connection timeout or a misconfigured email account.

To resolve this error, you can try the following:

1. Check the recipient address: Verify that the recipient address is correct and valid.
2. Check the domain name: Ensure that the domain name of the recipient's email address can be resolved.
3. Check the mail server configuration: Verify that the mail server's configuration is correct and that there are no issues with the DNS records or firewalls.
4. Check the email client or server: Restart the email client or server, or try sending the email again later.

If you're still experiencing issues, you may want to contact your email provider or IT department for further assistance.