SMTP error from remote mail server after RCPT TO:<email@example.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.
All popular mail servers have SMTP authentication enabled for security protection. Mail accounts using those servers need to authenticate first, before trying to send mails.
At times, users can try to send mails from their mail clients without enabling authentication. ‘550-Please turn on SMTP Authentication’ is a commonly reported error when users try to send mails without authenticating.
Often this 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 expert support technicians detect and resolve these issues.
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1. Improper DNS configuration
Domain migrations are common in hosting industry. Server upgrades or changes in provider can necessitate transferring a domain from one server to another.
But if the migration is not properly done, it can happen that the customer’s MX setting does not get updated to the new server.
It is also possible that users do not update their mail client settings properly. These issues would cause the mails to be sent to the old server, and the connections will be rejected.
In the servers that we manage, Bobcares technicians avoid such errors by following a detailed migration checklist and post-migration validation for all services.
Another possibility for ‘550-Please turn on SMTP Authentication’ is, when the customer uses a third party mail solution such as Google Apps as their mail exchange.
For mail servers that validate email sending domains using SPF records, this can pose an issue if the records are not updated to allow these external MX to deliver mails.
Mail server will reject the mails from those domains citing authentication issues. In the mail servers that we manage, we add the external MX IP into the SPF record of such domains to prevent this error.
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2. Missing local domain configuration
For a domain’s mail to work, it should have entries in the corresponding mail server config files. For instance, in Exim servers, there are two files – localdomains and remotedomains – to determine the domain’s mail server.
An account that uses local mail server should have its domain name listed in localdomains file. For domains with remote MX, there has to be entry in remotedomains file.
Due to any configuration mistake, the required entries can get messed up in these config files, leading to mail errors such as ‘550-Please turn on SMTP Authentication’.
We do a quick check of the domain’s mail configuration settings to identify such problems. To resolve it, we do a custom configuration allowing the mail gateway to relay mails to the destined mail server.
Bobcares’ website experts periodically audit the configuration settings of the websites they manage, which helps them detect and resolve such errors in no time.
‘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 listed above, has helped us save time in quickly restoring mail services. For resolutions to more common SMTP errors, see the full list here.