This box is used to turn SMTP integration “On” or “Off”.
You need to complete the details in the rest of the form before SMTP integration will work, but in any event SMTP will not work until this box is checked.
If SMTP integration is switched “On”, you can uncheck this box if you want to switch it “Off” again. You do not need to delete any of the other information in the form to switch SMTP integration “Off”.
Screen Shot - Use Custom SMTP