SMTP Error 455 is a permanent or "5xx" error code returned by a mail server, indicating the rejection of an incoming email message due to specific policy violations or other reasons. Unlike transient errors, SMTP Error 455 signifies a persistent issue that requires addressing the underlying problem.

SMTP Error 455 Examples:

• "455 5.7.1 Content blocked due to policy violations. Email flagged as spam."
• "455 5.1.0 Sender's domain blacklisted for abusive behavior. Contact administrator for removal."
• "455 5.5.2 Invalid recipient address recipient@example.com. Check recipient details."

What's Causing This Error?

SMTP Error 455 can stem from various reasons, including:

• Content policy violations: The email message contains content that breaches the recipient server's policies, such as spam, malware, or prohibited file types.
• Sender reputation issues: The sender's email address or domain has a poor reputation, possibly due to previous policy violations or spammy behavior.
• Invalid recipient address: The recipient's email address provided in the "RCPT TO" command or the "To:" field of the email message does not correspond to a valid email account or mailbox.

How to Resolve SMTP Error 455?

To address SMTP Error 455, follow these steps:

• Review email content: Ensure that the email message content complies with the recipient server's policies. Remove or modify any content that may be flagged as spam or malicious.
• Improve sender reputation: Address any issues related to the sender's reputation by adhering to email best practices and policies. Avoid sending spam or engaging in spammy behavior.
• Verify recipient address: Ensure that the recipient's email address is spelled correctly, is complete, and corresponds to a valid email account or mailbox.

‍