Just retesting HubSpot Free again after some years and discovered that HubSpot automatically adds a “Powered by HubSpot” the footer of each outgoing e-mail. There does not appear to be an option to switch off this silly behavior. This “feature” had neither been declared clearly before people register for the free editions, nor it is reasonable to expect users to delete that unwanted footer from each outgoing e-mail.
There must be an option to turn off the HubSpot branding in the free editions. It must be added soon.