Mail not being received

I’ve got everything working and I’m happy with it, the only problem is that some of the e-mails are not being received. Test e-mails sent from the plugin settings section work.

I’ve got my Elementor form set to send ‘Email’ to me and ‘Email 2’ should go to me and be CCed to the person who filled in the form (this is because if I just address it to them directly, the form doesn’t work [I get a ‘server error’ specifically about Email 2]).

The form works, I receive Email and Email 2 as expected, but the person filling in the form receives nothing. I’ve tried with TLS and SSL and the experience is the same.

This is true in Firefox, Vivaldi, Chrome and mobile Vivaldi browsers.

This is my server info:

OS: Linux bulma-lon.krystal.uk 4.18.0-513.9.1.lve.el8.x86_64 #1 SMP Mon Dec 4 15:01:22 UTC 2023 x86_64
PHP version: 8.5.2
WordPress version: 6.9.1
WordPress multisite: No
openssl: Available
allow_url_fopen: Enabled
stream_socket_client: Available
fsockopen: Available
cURL: Available
cURL Version: 8.14.1, OpenSSL/1.1.1w

Thank you for any advice you can give.

The page I need help with: [log in to see the link]