The error message "550 command rejected due to Sender ID validation failure" means that the recipient's email server rejected your email because it couldn't verify that your email server was authorized to send emails on behalf of your domain.

This issue usually occurs because your domain's Sender Policy Framework or SPF record is invalid or missing. An SPF record is a special DNS record that lists which servers are allowed to send emails for your domain. If your SPF record is incorrect or missing, the recipient's email server won't be able to verify that your server is authorized and will reject your emails.

To fix this, you need to update your domain's SPF record to include the correct IP address or domain name of the server that sends your emails. Adding this information to your SPF record will help the recipient's server verify that your emails are legitimate and not spam.

If you're not familiar with how to update your SPF record, contact your email provider or system administrator for help. You can also use online tools and resources to generate a valid SPF record for your domain.

Other factors like your email content or sender IP reputation can also impact delivery, so consider those as well if you continue to experience issues.
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