Actually, I've just discovered that the gmail one was coming through. It appears Mac Mail was hiding 'duplicates' and only displaying one. When I trawled through the individual accounts they were all there.
The other thing I've discovered FWIW is that when you're running Contact Form 7 on your website and you have your MX records set to use a 3rd party's, such as Google, you have to disable the mail service on your domain, otherwise there will be interference. That's even though there were no mail accounts set up. Once I switched off the mail service completely, the issue was fixed.