Error: Sending Test Email Notification Throws SMTPSendFailedException: 450

Symptom

1. Release’s SMTP Server was not able to send a test notification and throws Error 500, SMTPSendFailedException: 450 in the GUI:
   
2. In the Release's log, SMTPSendFailedException: 450 Error invalid sender domain or DNS temp failure can be found as shown in logs below:

2020-12-01 16:05:33.261 [qtp1904720585-38] {method=POST, request=/settings/smtp/
    checkConfig,username=johndoe} ERROR c.x.d.r.m.UnhandledExceptionMapper - 
    Unhandled Exception: {}

java.lang.reflect.UndeclaredThrowableException: null
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed
    (CglibAopProxy.java:759)
at com.ryantenney.metrics.spring.TimedMethodInterceptor.invoke(TimedMethodInterceptor
    .java:48)
at com.ryantenney.metrics.spring.TimedMethodInterceptor.invoke(TimedMethodInterceptor
    .java:34)
  …
Caused by: org.apache.commons.mail.EmailException: Sending the email to the following
    server failed : example.corp.exam.com:25
at org.apache.commons.mail.Email.sendMimeMessage(Email.java:1469)
at org.apache.commons.mail.Email.send(Email.java:1496)
  …
Caused by: com.sun.mail.smtp.SMTPSendFailedException: 450 Error: invalid sender domain
    or DNS temp failure
at com.sun.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:2374)
at com.sun.mail.smtp.SMTPTransport.mailFrom(SMTPTransport.java:1808)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1285)

Possible Root Cause

The SMTPSendFailedException: 450: Invalid Sender Domain or DNS temp failure is typically caused by:

• Release server unable to reach the SMTP Server due to a DNS issue
• Sender's Mail Addresses used in the From field is invalid, incorrect, or incomplete
• Tools like antivirus or firewall block the SMTP connection

As the specific root cause may vary from one SMTP server to another, we recommend you consult your SMTP server administrator and network team for specific troubleshooting steps needed. As for other Error codes related to SMTP Exception, please refer to IANA SMTP Status Codes Registry.