Custom Mail Handler from tutorial doesn't pick email

[Viktor Kuzmychov]

Hi everyone! 

I followed Mail Handler tutorial and installed plugin on my JIRA 7.12.1

It seems to work fine, every component is enabled (on add-ons page) and when I choose non-existing JIRA issue key it shows appropriate message. 

I've created a file in the /jira/import/mail directory which should represent an email, however plugin doesn't pick it up. 

I also downloaded sources of the same plugin from Bitbucket, compiled it and installed (my initial plugin used slightly different names, so it was ok). But that didn't work either. 

Does anyone know what exactly I am missing here?

Thank you!