Email Extension - Jenkins pipeline is unstable - email

Question

I have configured jenkins pipeline to send email to approval from PO when production deployment is made.
i have below code in jenkins file:
def notifyApprovers(inputStatus, emailBody) {
echo "${emailBody}"
sleep 10
withVault([vaultSecrets: [getEmailNotificationList()]]) {
emailext attachLog: false,
attachmentsPattern: 'example_file.yaml',
from: 'xxxx#ford.com',
body: "${emailBody}",
subject: "Production Deployment ${inputStatus} for RoadsideAssistance EU ",
to: "$PROG_DEPLOY_APPROVER_EMAIL_LIST"
}
}
Email is getting triggered successfully. But some times its throwing below error:
550 Not permitted
DEBUG SMTP: got response code 550, with response: 550 Not permitted
RSET
250 Reset completed
DEBUG SMTP: MessagingException while sending, THROW:
com.sun.mail.smtp.SMTPSendFailedException: 550 Not permitted
;
nested exception is:
com.sun.mail.smtp.SMTPSenderFailedException: 550 Not permitted
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)
at hudson.plugins.emailext.ExtendedEmailPublisher.sendMail(ExtendedEmailPublisher.java:524)
at hudson.plugins.emailext.EmailExtStep$EmailExtStepExecution.run(EmailExtStep.java:249)
at hudson.plugins.emailext.EmailExtStep$EmailExtStepExecution.run(EmailExtStep.java:182)
at org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution.lambda$start$0(SynchronousNonBlockingStepExecution.java:47)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.base/java.util.concurrent.FutureTask.run(Unknown Source)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.base/java.lang.Thread.run(Unknown Source)
Caused by: com.sun.mail.smtp.SMTPSenderFailedException: 550 Not permitted
at com.sun.mail.smtp.SMTPTransport.mailFrom(SMTPTransport.java:1817)
... 10 more
Not sent to the following valid addresses:
SMTPSendFailedException message: 550 Not permitted
Below is email extension plugin
[enter image description Email extension pluginhere](https://i.stack.imgur.com/lzgWU.png)
Any thoughts why its unstable.
Tired adding sleep but still unstable