Thats not exactly the case. - Receiving website contact form emails also have the branding, what do normal people to? Click Reply and answer to the client. So the footer will be part of the answer that is sent directly to the client.
I'm now trying to find a solution to configure my email server to filter it. It's offending me we are paing 170+$ monthly for a non-branded version and now wasting time on such issues ...