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When sending emails using the send email smart services, some will fails to be sent. The following error can be seen 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>]
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.
To avoid this error, here are some solutions that can be implemented:
This article applies to all versions of Appian.
Last Reviewed: March 2019