If the Process fails sporadically with error "com.sun.mail.smtp.SMTPSendFailedException: 451 5.7.3 Must issue a STARTTLS command first"
Stop the atom service & restart the atom.
Help document To Start, Stop or Configure an Atom Running as a Service
If the issue still persists after restarting the atom, please contact your mail exchange server admin to see if there any issue with SMTP server.
If the issue is not resolved after following above steps,please contact Dell Boomi Support to report the issue and we will help investigate further.