A crude, yet simple solution:
<p>Getting more information for class subject A, send a mail message using this <a href="mailto:youraddress@yourdomain.com?subject=Class%20subject%20A%20interest&body=I,%20<sender;s%20name>%20have%20an%20interest%20in%2the%20following:%0AClass%20subject%20A%0A%0AKind%20regards,%0A<sender%20name>%0A">link</a>.</p>
<p>Getting more information for class subject B, send a mail message using this <a href="mailto:youraddress@yourdomain.com?subject=Class%20subject%20B%20interest&body=I,%20<sender;s%20name>%20have%20an%20interest%20in%2the%20following:%0AClass%20subject%20B%0A%0AKind%20regards,%0A<sender%20name>%0A">link</a>.</p>
<p>Getting more information for class subject C, send a mail message using this <a href="mailto:youraddress@yourdomain.com?subject=Class%20subject%20C%20interest&body=I,%20<sender;s%20name>%20have%20an%20interest%20in%2the%20following:%0AClass%20subject%20C%0A%0AKind%20regards,%0A<sender%20name>%0A">link</a>.</p>
<p>It is also possible to send a similar request by post using our <a href="www.yourdomain.com/contact"><strong>contact form</strong></a> or by using the telephone number(s) listed in the form.</p>
If people have a (properly configured) mail client on their system, they will see a new screen appear with all the required information already filled into the receivers address, the subject and the body of the message. The only thing the prospect needs to do is clicking on the 'Send' button of their respective mail client. If they have configured gmail or other online mail client, that should result in a new browser tab to their online mail account with the same message content already pre-filled.
Creating a message with an automated subject line and/or mail address are easy to filter in your own mail client (workable if attendance numbers are low) or mail processor (if attendance numbers are high). Most mail clients have features that can automate responses, if you wish to send the prospect a confirmation mail of any kind.
As stated earlier, it is a crude solution and only really viable for a low amount of classes in the current format. But you can alter the message content, etc. as you please.
This solution also does not take into account users that have an improperly configured mail client or no mail client at all on their system. Something to consider as well.