Diagnostic-Code: smtp; 550-Please turn on SMTP Authentication in your mail client.

Email doesn't sent.
How do I turn on SMTP Authentication?

Try changing your Email Type setting to SMTP instead of mail.

Can you please let me know what I will need to do to ensure that the clicked is working.
At the moment, I have added a link into the email however when a user receives the email and clicks on the link, the report doesn't show that someone has clicked the link. Also, the spam report doesn't work.

I'll need FTP access to debug these issues on your server.

please find on the private message the details

That FTP information doesn't seem to work for me. Maybe you have IP restrictions in place. I can't even seem to connect to the server.

Please let me know your ip so I can white list it.
I have blocked all countries a part UK.
From which country you are trying to logon?
let me know and I will unblock your country so you can access the ftp

I'm in the US.

I have whitelisted your ip.
Can you please try again?

Ok I was able to find some issues with the mysqli update. I have fixed it on your site.