Hi @lukas.kindt,
Welcome to the Auth0 Community!
“Is there a way for me to check what happened to this email?” > You can check for errors in Logs in Auth0 Dashboard to see what happened to the emails.
“Or a way I can send him a link to reset the password?”
These articles detail what could be the possible cause of this issue and how it can be resolved:
I hope it helps!
Thanks,
Timotei