SMTP Error 459 typically occurs when a detailed error message is not provided, making it challenging to deduce the exact cause. However, users within the SMTP community have identified common reasons for this error, including invalid recipient emails or sender IP/email being on a deny list.

What's Causing This SMTP Error 459:

The SMTP error 459 can be attributed to:

• Invalid recipient email.
• Sender's email sending IP or email being on a deny list.

How to Resolve SMTP Error 459 - Step-by-Step Solution:

As the error message is generic and lacks specificity, here are steps you can take to troubleshoot and potentially resolve the issue:

• Verify Email Address:
• Ensure the recipient email address is valid and accurately entered.
• Verify IP Blacklist:
• Check if your sender IP is listed on a deny list using tools like MxToolbox. If your IP is listed, contact the relevant Domain Name System-based blocklist service and request removal of your IP from their deny list.

By following these steps, you can attempt to address SMTP Error 459, especially in environments like phpmailer and Jenkins.

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