An editor running with root privileges is required to edit the XML zone files. To view the files for previously configured zones, enter the following command as root:

~]# ls /etc/firewalld/zones/
external.xml  public.xml  work.xml

To remove a service from a zone, for example to remove SMTP from the work zone, use an editor with root privileges to edit the /etc/firewalld/zones/work.xml file to remove the following line:

<service name="smtp"/>

If no other changes have been made to the work.xml file, it can be removed and firewalld will use the default /usr/lib/firewalld/zones/work.xml configuration file after the next reload or system boot.