In all emails being sent out from my workflows, can I set the sender to a different email address?

Rethink Workflow allows the workflow designer to specify sender and reply-to for email communications being sent out from our system.

Set the sender and reply-to per workflow

To change the sender and reply-to per workflow, click on the VARIANT and scroll down to "Email Settings" section. 

Set the sender and reply-to for the entire organization

You can set the sender and reply-to for the entire organization in Company settings