5.3.0 other mail system problem 554 '5.6.0 invalid message content

A pesky error!

The error message "554 5.6.0 invalid message content" is typically returned by a mail server when it encounters an issue with the content of the email message being sent. Here are some possible causes and solutions:

  1. Invalid or malformed email headers: Check that your email headers are correctly formatted and don't contain any unusual characters or syntax errors.
  2. Invalid or malformed email body: Ensure that your email body is well-formed and doesn't contain any unusual characters, such as HTML tags or special characters, that might be causing issues.
  3. Attachment issues: If you're sending an attachment, ensure that it's a valid file type and not corrupted. Also, check that the attachment name and size are within the allowed limits.
  4. Character encoding issues: Make sure that your email content is encoded correctly using a standard character encoding scheme like UTF-8.
  5. Email client or server configuration issues: Check your email client or server configuration to ensure that it's set up correctly and that there are no issues with the mail server's configuration.

To troubleshoot this issue, you can try the following:

  1. Check your email client's logs: Look for any error messages or warnings in your email client's logs that might indicate what's causing the issue.
  2. Use a mail client that allows you to view the raw email message: Some email clients, like Thunderbird, allow you to view the raw email message. This can help you identify any issues with the message content.
  3. Use a mail server that allows you to test email sending: Some mail servers, like Mailgun, offer a testing feature that allows you to send test emails and check for errors.
  4. Consult your email provider's documentation: If you're using a third-party email service, consult their documentation to see if they have any specific requirements or restrictions for email content.

If none of these solutions work, you may want to consider seeking further assistance from your email provider's support team or a professional email administrator.