You mention email handlers which implies you are looking at a Jira Software or Work Management project, not a Service Management one. Jack has already said where to look for those.
For email handlers, you'll need to look at the configuration of the handler. by going to it in global administration. There could be all sorts of things wrong with the route though, and you'll need to look at the whole thing - from "can this person send email to this email address" through what the handler is set up to do with incoming email, and then "does this user have the create issue permission in the target project"
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.