replied on February 10, 2021
In order to handle it properly I recommend sending emails with Workflow instead of the Forms Email activity. This is because workflow has a try catch option to test the email and notify you if there is a problem. Also, by using workflow you can both be notified and be given a chance to directly edit the email and retry without messing around with the database.
It is a lot of work to setup but solves the problem.
Your forms process would work like this.
Submission > Call Workflow to test email > Workflow returns Success/Fail
If Success then continue, If Fail then assign a user task to correct the email address and loop back around to calling the workflow.
By assigning the task using a form that contains the email variable, you can edit it directly and retry. You can also include a notification with the task assignment.