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Smtp server returned 530 MustIssueStartTlsFirst exception occurs when using Server-Side Synchronization

This article helps you fix an issue in which you get the "Smtp server returned 530 MustIssueStartTlsFirst exception" error when using the Server-Side Synchronization with a POP3/SMTP profile in Microsoft Dynamics 365.

Applies to:   Microsoft Dynamics CRM 2016
Original KB number:   3214706

Symptoms

When you test and enable a mailbox in Dynamics 365 (formerly known as Dynamics CRM Online), you encounter one of the following errors in the Alerts area:

The email message "Test Message" cannot be sent because an error occurred while establishing a secure connection to the email server. Mailbox <Mailbox Name> didn't synchronize. The owner of the email server profile <Email Server Profile Name> has been notified.

Email Server Error Code: Smtp server returned 530 MustIssueStartTlsFirst exception.

ActivityId: <GUID>
>Error : System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpTransport.EndSendMail(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)

Email cannot be received for the mailbox <Mailbox Name>. Make sure that the credentials specified in the mailbox are correct and have sufficient permissions for receiving email. Then, enable the mailbox for email processing.

Email cannot be received for the mailbox <Mailbox Name>. Make sure that the credentials specified in the mailbox are correct and have sufficient permissions for receiving email. Then, enable the mailbox for email processing.

Cause

This error can occur if you are using a POP3/SMTP email server profile and one of the following issues exist:

  1. The user name or password isn't correct.
  2. If you are using Gmail, the option to allow less secure apps is disabled.

Resolution

  1. Verify the User Name and Password values on the mailbox record in Dynamics 365 are correct. The error includes a link to the mailbox record in Dynamics 365.

  2. If you are using Gmail, verify the Allow less secure apps option is enabled:

    Less secure apps & your Google Account

After changing any of the settings mentioned above, click Test and Enable on the mailbox record again.

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