How do I remove mention of the main site from emails sent to clients via a sub-site?

When visitors to a subsite on my network complete contact forms, the message comes from the network on behalf of the subsite. I want to remove this feature, so the email comes directly from the client.
I have a multisite network and when my clients get contacted through the contact forms on their site, the message reads as "no-reply@mainsite.com on behalf of Person's Name (wordpress@subsitedomain.com - How do I remove mention of the main site from emails sent to clients via a subsite?