A pure text url in an email can be converted directly bu the email client, but the url can be added to some words, like clieck here and it should be clickable. If not, it’s the email client “not trusting” the email and disabling the links.
You can try to send the email to other clients (like gmail, yahoo, …) to check the differences. Since the standard confirmation message is the same for every installation, the problem should be in your client otherwise it wouldn’t be clickable for every one.
Can you do such a test?