If you log into your CPanel and click on "Track Delivery" in your email section. You will see the outgoing email server is blocking the delivery with the message:
ECDHE-RSA-AES256-GCM-SHA384:256 CV=yes: SMTP error from remote mail server after end of data: 550 5.7.1 [CS] Message blocked. If this is a false positive, please report this to your hosting service provider. See https://console.mailchannels.net/insights/bounce?auid=9wt3zsp42r&sender=mail%40manchestermassage.co.uk&txid=6b8be04d786167ac
It has something to do with the content in the email body, since I can get the email to go through by changing the email body and putting in a simple message. I'm not sure how to identify the exact issue with the email body, but you would probably have to edit it to get it to go through. Another option would be to switch hosting providers or move to a dedicated hosting plan that has it's own SMTP server.