SMTP error from remote mail server after RCPT TO:<user@domain.com>: host domain.com [xx.xx.xx.xx]: 550-Please turn on SMTP Authentication in your mail client. 550-(mail.server.net) [xxx.xxx.xxx.xxx]:36825 is not permitted to relay through 550 this server without authentication.
If you have SMTP authentication enabled in your server, this would be a common error reported by your mail users. Often the issue is resolved by enabling SMTP authentication settings in the customer's mail clients.
However, there are 2 other less obvious reasons for mails to bounce with this error. Here's how our help desk support team detects and resolves these issues.
1. Improper DNS configuration
When a domain has been recently transferred in from another provider (or even from another server of the same provider), it is likely that the customer's MX setting was not properly updated. This would cause the mails to be sent to the old server, and the connections will be rejected. Setting the MX IP to the current server fixes this issue.
Another possibility is when the customer uses a third party mail solution such as Google Apps as their mail exchange. If the SPF (Sender Policy Framework) records are not updated to allow the external MX to deliver mails, the mails will be rejected citing authentication issues. A quick addition of the external MX IP into the SPF record fixes this. For eg., in the case of Google, the following SPF record works:
v=spf1 include:_spf.google.com ~all
2. Missing local domain configuration
In cases where the customer uses an external incoming mail gateway, it is possible that the domain may not be listed as a local domain in the host mail exchanger. For eg., if the domain is hosted in server1.net, it should have a mail server setting listing it as a local domain of server1.net. However, some auto-configuration scripts tend to delete this entry when the domain's MX points to an external IP (like a mail gateway).
A quick check of the domain's incoming settings, and POP settings reveals this problem, and the solution involves a custom configuration allowing the mail gateway to relay mails to the host mail exchanger.
550-Please turn on SMTP Authentication is usually reported from mail accounts in cPanel/WHM servers, and Microsoft Exchange servers. As mentioned earlier, in the vast majority of cases, the issue is resolved by enabling authentication in the customer's mail clients (like Microsoft Outlook, Outlook Express, Thunderbird, etc). However, keeping an eye out for the other possibilities has helped us save time in quickly restoring mail services.
For resolutions to more common SMTP errors, see the full list here.
Knowledge of the common causes of an issue saves time in restoring a customer's email service. Bobcares helps webmasters quickly resolve email service errors, thereby minimizing business downtime.