Email Smart Service unable to send email in 18.3

On our On-premise 18.3 we changed our email service from on premise to Office 365 exchange and made the required changes to custom.properties file for email delivery. However we are able to receive user password reset, system alerts, task alerts without any issues but email sent by smart service is not being sent. I have checked the mail-listener logs, unattended-request-poller logs but no error messages are written to them. Are there any other log files that needs to be checked?

Update: I checked our SMTP relay server and i see failure logs as the appian environment is a .lab domain and the email server is configured as .com domain. So i created a new email XML as suggested in https://docs.appian.com/suite/help/18.3/Configuring_Custom_Email_Senders.html but the smart email service is still not referring to the email custom email  xml. Any help to fix this would be helpful

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