I have seen multiple times errors in workflows or plugins that send emails regarding the fact they can’t send emails on behalf of others, this is because the user configuration is not set to allow this functionality. To allow other users to send emails on your behalf follow the steps below:
Go to “Options” in the upper right corner:
Click on “Email” section and check the option below:
NOTE: Try to keep track of the emails that are send in your behalf and what is being send for security purposes.
Hope it helps.