Form Submission Error - Sender Email not auto populating

My client uses Outlook email. All of his form submissions go into Outlook but when he goes to reply to those requests, the sender email doesn't auto populate in the "To" field.  He has to drop down into the actual form to retrieve the sender email in order to respond back. The auto populated email address is "no-reply@squarespace.info"

Anyone know why that would be? Is there a setting inside Outlook maybe? I operate with Gmail and everything runs through SQSP. I don't have this issue so I'm not sure why it's happening for him. The only thing I can think of is that it has something to do with Outlook settings.