Why I haven't received the activation email yet?

If you've completed the signup process and you haven't received the verification email yet, then you need to check your Spam folder because sometimes it is being filtered like spam.

Also, note that we use Mailgun to deliver our emails. So, if the server blocks in any way email that originates from Mailgun.org or it is implementing some kind of greylisting, so you need to whitelist transifex.com.