The following scenarios can cause outgoing emails transmission to fail.

Connectivity issues are normally caused by an obstructive firewall or a network connectivity issue. Firewall issues might be caused by incorrect settings or software conflict that leads to the firewall blocking data entry. Network connectivity issues might occur in either the on-premises network or in the cloud, these issues might result from defective physical components that are necessary to establish a connection or from incorrect settings. SSL/STARTTLS configuration issues might also lead to network connection failures.

1. Test the connection to the outbound (sender) email server:
   Successful connectivity tests do not guarantee proper behavior during run time. Testing connectivity is only the first troubleshooting step.
   1. Save your changes to the email account.
      Connection testing uses the email account information saved in the form both for new email accounts and for updates to existing email accounts.
   2. For outbound email, in the email account form, click the Test Connectivity button for the sender.
   3. If the connectivity test fails, review the Message field in the Receiver Test or Sender Test window.
   4. If Message field does not identify the root cause of the problem, check the Debugging information section for JavaMail that is provided at the bottom of the test connection dialog box.
   5. If the Debugging information section does not identify the root cause of the problem, test the email connection by using a third-party email client such as Thunderbird.
   6. Verify whether the issue is specific to Pega Platform by testing the connection from the same server that hosts your application.
2. If you experience network connection issues due to problems with your on-premises network, contact your system or network administrator and check the following parameters:
   1. Check the correct settings for host name and port, and credentials for the email provider.
   2. Check whether the firewall software and settings are set up correctly.
3. If you experience network issues in the cloud-side of the network, contact Pega Support to check the following parameters:
   1. Check the correct settings for host name and port, and credentials for the email provider.
   2. Ensure that the connection credentials are correct by testing the email connectivity port.
4. If you experience network connection failures due to SSL/STARTTLS configuration issues, contact your system or network administrator and check the following parameters:
   1. Verify that your computer is connected to an SMTP server over a secure connection.
      SMTPS or secure SMTP uses TLS/SSL to secure the network connection between your email client and the server.
   2. Verify that the IP addresses of your nodes are on the safe recipients list.
      If the IP addresses are blocked, the SMTP connection from those nodes fails.
   3. Verify the spelling and validity of your passwords.
      Any incorrectly spelled or expired passwords cause authentication failures.
   Even if the test connectivity is successful, the SMTP server might block the sender for various reasons, for example:

   • The email account is new or has not been used for some time and requires verification with the provider to enable sending from external servers.
   • The Send As email address has not been used on the SMTP server before and must be registered with the provider to enable outgoing email.
   • The user's email service (Hotmail, Windows Live, their ISP's SMTP server) does not trust the sender's email reputation.

When emails are put into an SMTP queue, which provides temporary storage before the emails are processed, outgoing asynchronous email messages fail to send.

1. When sending asynchronous email messages, ensure that the Queue Processor (pySendEmail) functions, and then check the error queue for failed messages.