Before you change this setting please be aware of the following:
If you have a lot of cancelled events, there is no need to worry if you see a bunch of service mailings being prepared by the system in the module Automated mailings.
Just before an automated mailing will be sent the system will check the status of an event.
If the event is cancelled the service mailing won't be sent. So if this was the reason you wanted to stop the automated mailing, you don't have to do so. The system will automatically recognize the called event and won't send the servicemail.
This is the part that you are looking for. This is the setting that generates automated servicemails.
Delete the word that says: "Servicemails" [delete the word and also the comma].
Don't forget to scroll down and click save.
Now the system will not generate any new service mails.
Just one more thing!
The system is generating automated mailings in advance. How many days in advance is different for every theatre, and also defined in the Core module.
Dashboard > Mailings > Automated Mailings
Here you can see all the mailings that have been created in advance. You will have to delete them manually if you don't want them to be sent.
After doing this no new automated mailings will be created.