I had a similar situation once. Here's what I remember:

The mail was HTML, but the link wasn't clickable. (I cannot recall if it wasn't because there were no <a>-tags around it or because the mail client wouldn't recognise them). Anyway: I could not copy&paste it from the inbox. Worse: I couldn't copy&paste it when I opened a reply; somehow the original text within the reply could not be edited or clicked or copied.

I then clicked settings > applications > mail. There's an option that controls how HTML mails are handled. you can switch HTML off so that HTML mails are displayed as plain text. That's what I did. returned to the mail client, re-opened the mail and - voilà! - the mail client rendered the URL as a clickable link.

"One simple gesture."