Here is the way you can add multiple recipient in the spool list for background jobs;
Transaction code: SO15
Here you have an option for creating private or shared distribution list, for adding multiple recipients, select the option of shared distribution and click create icon;
You will be taken to new screen where you would be required to enter distribution list name, title, folder where you want it to be stored and check whether this is a Subscription list or not.
Note: you can create your own folder if you don’t want to use an already existing folder.
Next you need to click on “Distribution list content”
On this screen you can enter all the recipients email ids which you want to include in your list.
This is the way you can create a shared distribution list.
Now while creating a background job in SM36, you can enter the list name in the spool list recipients, which will ensure all the recipients receive mail for job completion.
Hope this helps;