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DRAFT KB-XXXX Send email fails for some processes

Symptoms

When sending emails using the send email smart services, some will fail with the following error present on the application server log:

ERROR com.appiancorp.ap2.mail.Mail - Could not send mail via <SMTP_SERVER>:<smtp_port> to
ERROR com.appiancorp.process.runtime.activities.SendEmailActivity - com.sun.mail.smtp.SMTPSendFailedException: 432 4.3.2 STOREDRV.ClientSubmit; sender thread limit exceeded [Hostname=<HOSTNAME>]
com.sun.mail.smtp.SMTPSendFailedException: 432 4.3.2 STOREDRV.ClientSubmit; sender thread limit exceeded [Hostname=<HOSTNAME>]

Cause

This error appears when using Microsoft Exchange Online. Since June 1, 2018, their SMTP Authenticated Submission protocol has been changed in order to only allow three concurrent connections to the service per mailbox. Additional connections are rejected with the above error.

The complete documentation regarding this limit can be found on this page.

Action

To avoid this error, here are some solutions that can be implemented:

  • Use another mail server that is designed to send large amounts of emails.
  • If the issue is happening on a Cloud environment, use the mail server provided instead of an on-premise one.

 

Affected Versions

This article applies to all versions of Appian.

Last Reviewed: March 2019