JIRA's standard mail handlers can only create issues in one project - it has no way of knowing how you might define the project in an email.
You need add-ons that can provide handlers that will be able to implement the logic you need to perform to make the decisions on which project is needed. You can write your own, or try out something like JEMH or JETI.
I thought so too, but JIRA documentation(https://confluence.atlassian.com/adminjiraserver071/creating-issues-and-comments-from-email-802592933.html) says : "
I have multiple projects that use variations of the same base workflow. The variations depend on the requirements of the project or issue type. The variations mostly come in the form of new statuses ...
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