Not to nitpick but being emailed a temporary password in cleartext doesn't seem like an issue to me, assuming you're required to change it as soon as you log in.
Especially since that email address presumably is used for the forgot password authentication anyway.
But it is at least the equivalent of a code smell. perhaps a "UX smell"?
A couple of obvious ways it can go bad: An attacker could potentially have access your email (perhaps from a data breach elsewhere or a password stuffing attach) and use the temp password before you do. If the temp password is the one entered by the user during signup, a naive user could sign up using their commonly-reused-password which then sits in cleartext foreven in their email archive.
