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2 non-obvious reasons for “550-Please turn on SMTP Authentication” error in cPanel & Exchange servers, and what to do about them

by | Aug 20, 2016

SMTP error from remote mail server after RCPT TO:<>: host [xx.xx.xx.xx]: 
550-Please turn on SMTP Authentication in your mail client.
550-( []: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.

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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.

In short..

‘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.


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  1. Hi I recently moved to Hostgator and my domain registrar is GoDaddy. Mail was configured on google apps. Now I am getting same error when anyone sends me an email. How I should rectify it?

    thank you

    • Hi Pavan,

      I’d recommend you start with checking your MX records. Looks like GoDaddy has set your domain’s MX to the servers in which your website is hosted.

      If you are still facing any trouble, please let me know your domain name, and I’ll take a look from here.

  2. Ah yes…thanks for the reminder “it is possible that the domain may not be listed as a local domain in the host mail exchanger”.

    Heads up for others, if you change the MX records to point to your server and in cpanel the host mail exchanger is listed as automatic, you may need to set it to local.

  3. Hi ,

    I am trying to setup my mail id into ZOHO, but got the error msg , Mail sent = DONE, Mail recv = Bounce

    My mail id is

    I am unable to recv any mail
    I was configure Cpanel Mx record properly
    already check with MXtool

    Can you please help me .


    • Hi Jhimli,

      I tried initiating an SMTP session for with your MX

      Your MX said that is not configured to accept connections in that server. Here’s the relevant SMTP log.

      rcpt to:<>
      550-The mail server could not deliver mail to
      550-The account or domain may not exist, they may be blacklisted, or missing
      550 the proper dns entries.

      Can you try re-creating the mail account in

      If you’re still facing trouble, please open a technical trouble request by clicking on “Contact Us” below.

  4. When sending mails I am receiving the below error
    550 5.1.1 Policy Rejection – Too many spam mails.Please try later[626

    Pls advise any solution

    • Ram,

      We would have to inspect your mail server for the spamming investigation and then suggest an appropriate solution. Please feel free to contact our 24/7 support team here – – for assistance.

  5. I had this same problem and its solved for me…what i did was

    I actually chose the Remote Mail Exchanger option from the WHMS under Edit DNS….and then i logged into the Cpanel and MX Entry section and chose the Local Mail Exchanger…hooo its working since then…thanks to Steve’s saved my day 🙂

  6. Unni/All, this seems to have wored for me! thank you!

  7. i configured zoho mail for my domain i can send mail to other domains but i can’t receive mails from other domains please find me solution

    • Ram,

      Your issue could be related to DNS settings, IP blacklisting or email client settings. Please contact our mail experts at to get the issue resolved, if it persists.

  8. It was my problem for this couple months, but I solved my problem by:
    1. Open CP (my ver. is 68.0.23)
    2. Go to Email Routing
    4. Click CHANGE


    It worked well now!

    • Semmy,

      Thanks for sharing your updates.

  9. I’m unable to send mails to email accounts on the same domain using outlook 15. i can send and receive from other domains but i get “550 required for authentication” whenever i send mails to accounts on the same domain. can you please help?

    • Hi Olalekan,

      The issue could be due to incorrect email configuration for the domain. Please contact our support team at if you still face issues. They’d help you resolve it.


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