Sorry, so I visited https://www.mail-tester.com and it gave me the e-mail address email@example.com to use, which I've inserted into the form script.
One obvious question though....the form script is blocking Yahoo, Hotmail and AOL so it won't ever reach firstname.lastname@example.org so how can it diagnose what's going wrong?
Sure enough, when I go back to https://www.mail-tester.com it doesn't display anything and just continually counts down from 15 without ever showing any results.
It's the form script that's blocking things because the form script provided by the host, albeit being very basic, doesn't block those domains.
I don't want to change all of my form scripts to that though because I like the WebAssist extension. There is clearly a problem with it though.
Hope you can help. Thank you.