SMTP error 556 signifies your email was permanently rejected (5xx) due to problems with the sender's email address or domain (phpmailer, jenkins). This indicates the message couldn't be delivered because of sender information issues.

What triggers SMTP Error 556?

Common scenarios behind SMTP Error 556:

1. Nonexistent Sender: The sender's email address ("MAIL FROM" or "From:") is invalid and doesn't correspond to a real account or mailbox (phpmailer, jenkins).
2. Invalid Sender Domain: The sender's email domain (e.g., example.com) is non-existent, expired, or has DNS (Domain Name System) issues.
3. Unauthorized Sender: The sender's domain or address cannot send email to the recipient, or it's blocked by their server for policy reasons.
4. Content Filtering: The email content might contain prohibited elements like spam, malware, or violations of the recipient server's policies.

What’s Causing This SMTP Error 556 In Your Servers?

Potential causes of SMTP Error 556:

• Verify Sender Address: Double-check that the sender's email address is accurate, complete, and belongs to a valid account or mailbox (phpmailer, jenkins).
• Check Sender Domain: Confirm that the sender's email domain is functioning correctly, has no DNS issues, and isn't expired.
• Contact Sender Administrators: If the sender's domain has issues, their administrators might need to intervene to resolve technical problems or adjust email sending policies.
• Review Email Content: Analyze the email for potential policy violations like spammy content, excessive attachments, or malicious links.

How to Resolve SMTP Error 556 - Step-by-Step Solution

1. Verify Sender Address: Ensure the sender's email address is accurate, complete, and belongs to a valid account or mailbox (phpmailer, jenkins).
2. Check Sender Domain: Confirm that the sender's email domain is functioning correctly, has no DNS issues, and isn't expired.
3. Revise Email Content: Address any potential policy violations in the email message, such as removing spammy content or harmful attachments, to comply with the recipient server's policies.
4. Contact Sender Administrators (if applicable): If the issue lies with the sender's domain, contact their administrators for assistance.

SMTP Error 556 Examples

• "556 5.1.1 sender@example.com: Sender address does not exist."
• "556 5.4.5 sender@example.com: Domain name not found. Check sender domain."
• "556 5.7.0 sender@example.com: Unauthorized sender. Email blocked due to policy reasons."
• "556 5.1.2 Content filtering detected prohibited content in the email message. Delivery denied."

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