In the mandrill templates:

  • EN–InvitationNewUser
  • EN-ResetPassword

A link to set/reset password is located, in some environment the default tracking in mandrill is not desirable so this can be disabled by adding the following link tag - mc:disable-tracking 

So it could look something like this:

<td height="70" style="text-align: center; font-family: verdana; font-style: normal; font-weight: bold; font-size: 18px;">#1 : <a href="*|ActivationLink|*" target="_self;" mc:disable-tracking>Click to activate your account</a></td>