/usr/lib/firewalld/services/ Current File: //usr/lib/firewalld/services/smtp-submission.xml

<?xml version="1.0" encoding="utf-8"?>
<service>
  <short>Mail (SMTP-Submission)</short>
  <description>SMTP-Submission allows remote users to submit mail over port 587.</description>
  <port protocol="tcp" port="587"/>
</service>