Help Center

its an email that links your howrse account to your own email. Check your spam folder. Also it opens up the option to pass buy. But there have been issues with it in the past so if its not shown up in 24 hours contact "contact us" at the bottom of the web page.

To verify your Howrse email address, click the verification link sent to your inbox during registration. If missing, check your spam/junk folder, the verification mail often tends to end up there.
Or go to your account settings to request a new validation email.
Verification is required to unlock features like selling horses for passes.

If you find the mail, click the link that is in there to verify your email address.