This KB Article describes steps to send email to multiple users in one go by executing the Automation Services Send Email Job functionality

How to Send email to multiple recipients (list of people) via Automation Send Email Job Builder on server and as well execute locally.

In Automation Services Job Builder > Send Email Task, there is an option to send the same email to multiple recipients (user list) in one go. For this you need to add comma(,) separator or in some use case semicolon(;) separator after each recipient email id. 

The type of separator that will work in your case depends upon your computer's local regional settings. 
You can find this setting under Control Panel>>Clock and Region>>Change Date, Time, or Number Formats. Go to Advanced Settings, under the Numbers tab you will find out the option name List Separator: and its value. that would be either semicolon or comma as a separator. Please find the below GIF for reference.



For Example:- if the separator is a comma(,) then you can write multiple email id with comma-separated like abc@tibco.com,def@tibco.com,ghi@tibco.com
and if the separator is a semicolon(;) then you can write multiple email id with comma-separated like abc@tibco.com;def@tibco.com;ghi@tibco.com