Thank you so much for stopping by with your suggestion. Zapier does look a bit complex but I'm willing to go with it if it helps. About spoofing, I get what you mean. Don't worry, this is not that.
Here are more details of what we need:
Basically, our management receives Enquiries via our Squarespace form since about a month ago. They are used to see clearly what the email is about. So when they receive them, they don't want to see
Subject: 'Form Submission - Contact Form'
Instead, they would prefer to see
From: 'firstname.lastname@example.org' or 'Enquiries'
Subject: 'Contact Form' or 'Enquiry form'
they are even ok with From: 'FW: Form Submission - Contact Form'
Even if all enquiries read like that it's ok, as long as it is clear for them at a glance what the email is about.
I have tried creating a Gmail account to receive the form submissions and forward them, but Gmail's 'forwarding' just redirects email, so they look just like the original Squarespace emails.
I'm sort of at a loss now. Despite how happy they are with our new SS website, they are really annoyed with the way they receive email now.
Let me know if you need any more details. Hope the above helps better explain my case.