Question:
In a workflow, how can I reference a keyword field which contains a list of email addresses for use with an Email Send step?
Answer:
In order to send out emails based on a list of email addresses contained in a keyword field, please refer to the following guide on how this can be accomplished.
The following is an outline of a workflow, and the steps involved where a keyword field contains a list of email addresses, then is iterated through so that an email is sent for each entry in the keyword field.
We'll need the following global variables created;
Text Data Type
Email
Integer Data Type
Count
Total
The first step is to create an Assign data step where we first initialize the Count global variable and give it a fixed value of 0.
Next, we'll create another Assign data step where we set our 3 global variables. 
For the "Email" global variable, we're going to grab the first email address stored in the keyword field.
This is accomplished by using this arithmetic expression when we first reference our keyword field. Next to it, we're referencing our Count variable which was set to 0.
In this case, 0 corresponds to the first line of the keyword field. 
For the "Total" global variable Arithmetic expression, we're using the Count function. We are also providing the keyword field as our parameter to return a total count of how many email addresses are stored.
Finally, we'll update the "Count" global variable by incrementing it by 1. 
After initializing the global variables and updating the Count global variable, we proceed to the Email Send step which will send out the email.
Now, a Condition step will be used in order to check if there are still any remaining email addresses which need an email to be sent to.
If there are, it will loop back to the second Assign data step then repeat the process above.
Once all email addresses have been sent, the workflow will end.
This is a simple case, but the logic should be able to be implemented in any workflow you have setup.
KBA applicable for both Cloud and On-premise Organizations.