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Understanding and Resolving the "550 Please turn on SMTP Authentication" Error

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By Dennis Nind

July 3, 2023

When sending emails, you may occasionally encounter an error message stating, "550 Please turn on SMTP Authentication." This error occurs when the email you're trying to send is flagged by our spam detection procedures. This guide will help you understand why this happens and how to resolve it.

Why Does This Error Occur?

SMTP authentication is a security measure used by mail servers to verify that incoming messages are from authorized users. If SMTP authentication is not enabled, the server may reject incoming messages, resulting in the "550 Please turn on SMTP Authentication" error.

How to Enable SMTP Authentication

Enabling SMTP authentication can often resolve this issue. Here's how to do it in various email clients:

Outlook Express

  1. From the Tools menu, choose “Accounts.”
  2. Select the “Mail” tab.
  3. Double-click the email account you need to update.
  4. Select the “Servers” tab.
  5. Check the box next to “My Server Requires Authentication.”
  6. Click “Ok.”

Outlook ’98 and 2000

  1. From the Tools menu, choose “Accounts.”
  2. Select email account you need to update.
  3. Click “Properties.”
  4. Select the “Servers” tab.
  5. Check the box next to “My Server Requires Authentication.”
  6. Click “Ok.”

Outlook 2002 and 2003

  1. From the Tools menu, select “Email Accounts.”
  2. Select “View or change existing email accounts” and click “Next.”
  3. Select your Email account and click the “Change” button on the right.
  4. Click the “More Settings” button in the bottom-right corner of the E-Mail Accounts window.
  5. In the Internet Email Settings window, click the “Outgoing Server” tab.
  6. Check the box next to “My outgoing server (SMTP) requires authentication.”

Outlook 2007

  1. From the Tools menu, select “Account Settings.”
  2. Select your Email account and click the “Change” button.
  3. Click the “More Settings” button in the bottom-right corner of the E-Mail Accounts window.
  4. In the Internet Email Settings window, click the “Outgoing Server” tab.
  5. Check that the box next to “My outgoing server (SMTP) requires authentication” is checked and “use same settings as my incoming mail server” is selected.

Outlook 2010

  1. From the File menu, select “Info” and choose “Account Settings.”
  2. Select your Email account and click the “Change” button.
  3. Click the “More Settings…” button in the bottom-right corner of the E-Mail Accounts window.
  4. In the Internet Email Settings window, click the “Outgoing Server” tab.
  5. Check that the box next to “My outgoing server (SMTP) requires authentication” is checked and “use same settings as my incoming mail server” is selected.

Mac Mail for OS X

  1. Open Mac Mail.
  2. From the “Mail” menu, choose “Preferences.”
  3. Click the “Accounts” icon at the top of the window.
  4. Next to “Outgoing Mail Server (SMTP):” click on the drop-down menu and go to “Edit SMTP Server List”
  5. Check to make sure you have the correct SMTP server selected at the top.
  6. Verify that “Authentication” is set to “Password.”
  7. If the “User Name” and “Password” fields are not set, enter your full email address as the username, and your password.
  8. Click “Ok.”
  9. Close the accounts window by clicking on the red circlein the far upper left hand corner of the “Accounts” window.
  10. Mac Mail will ask you if you wish to save your changes, make sure to click the “Save” button.

Other Possible Causes of the 550 Error

While enabling SMTP authentication can often resolve this issue, there are other potential causes to consider:

Improper DNS Configuration

Domain migrations can sometimes lead to issues with SMTP authentication. If the migration is not properly done, it can happen that the customer’s MX setting does not get updated to the new server. This could cause the mails to be sent to the old server, and the connections will be rejected.

Another possibility 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.

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'. To resolve it, we do a custom configuration allowing the mail gateway to relay mails to the destined mail server.

By understanding the cause of the "550 Please turn on SMTP Authentication" error and following these solutions, you can improve your email deliverability and reduce the likelihood of your messages being incorrectly marked as spam.

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