Email send error

I’m using Contact form 7 with a drop down box for recipients.

At the moment I’m getting this message when I click the submit button:
Failed to send your message. Please try later or contact the administrator by another method.

The code on the contact form is this:
<p>Your Name (required)
[text* your-name] </p>

<p>Your Email (required)
[email* your-email] </p>

<p>Subject
[text your-subject] </p>

<p>Your Message
[textarea your-message] </p>

<p>Who do you want to contact
[select your-recipient “[email protected]”
“Head [email protected]”
“[email protected]”
“[email protected]”] </p>

<p>[submit “Send”]</p>

Can you give me some ideas as to where to start looking for the error which is causing this?

The link to my test site is this https://www.s506439810.websitehome.co.uk/warriorswordpress/ and the Contact Form is reached by clicking the Contact Us link in the left hand sidebar.

https://www.ads-software.com/plugins/contact-form-7/