I tried accessing the mail server you have entered using telnet:
telnet mail.sports-injury-physio.com 25
and got back an error that it could not connect to the server, so I don't think that address and port combination is valid. you should contact your host for details on the email settings you should be using for sending an email using a PHP script.
it may be that they wont support the standard mail object, and you will need to use the Pear Mail for SMTP object, but you need to get that information from them.