When sending emails using the Send Email Smart Service, some emails fail with the following error present in 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. As of June 1, 2018, Microsoft's 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 here.
To avoid this error:
This article applies to all versions of Appian.
Last Reviewed: August 2019
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