Currently it is not possible to call up an email from sticky note.
If you wish to call up a file from a note then you would need to add the file link to the sticky note. Click on the top left button on a sticky note and choose Links. Once you add files there you would be able to launch it from the note from the toolbar (you would see a new button there to open the linked file).
Also if you drag and drop the file into the sticky note, it will create a hyperlink inside the note so that you can easily open the document.
This short video will give you more clarity on this:
I guess you wish to automatically associate the sticky note when you actually stick the note to that document or email. This is not possible as Notezilla displays the note based on the title of the window it is attached to (not the file or email itself).
We are planning to create plug-ins so that it serves the purpose. Currently, we cannot commit any date for it.