The messages are not even arriving in user's junk email.

What score do you get here ---> https://www.mail-tester.com/

If you have good score like 10/10 on https://www.mail-tester.com/ i would go to next step and sign up here ----> https://www.sendforensics.com and monitor you outgoing emails and sendforenics can see what issues you have with hotmail and gmail and others emails adresses and you email reputation. they will monitor eveyrthing and give you a score on you outgoing emails when it comes to content and many things that will make you email have perfect setup for good deliverity 

if this two suggestions not helps i would go for host you email from one of this host https://iwantmyname.com/services/email-hosting/ it did help me alot after leave my website server as host for my emails i get much better deliverity. and offcourse NEVER forget use SMTP for always clean you website from people that report you emails as spam and remove hard and soft bounces from you website every week and day for keep good reputation. And if you smart remove unsubscribtions to from you site that helps you have a very active website and not half dead

Thanks for the hints, I'm stuck in London at the moment so can't do an awful lot right now but I will get on top of this as soon as I can.

My email isnt even being received by the email testing site to give me a score although I am still getting the notice that the emailed was rejected by a local scanning code.

During my investigation I did get this debug notice if anyone can help?

Problem solved by enabling SMTP on the site.

great to know you solved it :)

As you guys are talking about scanning something then why not buy the https://obdcore.com/best-obd2-scanner-for-bmw/ at very low and reasonable prices. Just have it as soon as possible.