How and where do upload files get processed?

How does CF7 technically process uploads?

Say, I have a form with one upload field with a 3mb limit and a submit button. I set a notification mail for this form. (1) A visitor opens the upload selector and selects a local 3mb file. (2) She then clicks on submit. (3) She gets a spinner telling her that her upload is processing. (4) She gets an okay message once the submission is completed. (5) The admin receives a mail with her form submission including the uploaded 3mb file.

My questions:
When (1-5?) and where does the 3mb upload gets saved temporarily on the admin’s server?

Here is what I think and tested so far:
– I think the uploaded file gets saved temporarily in the visitor’s browser in (1)
– Once she clicks submit in (2) the file gets uploaded to the temp folder /wp-content/uploads/wpcf7_uploads. This upload is complete in (4)
– CF7 uses the temporary file to assemble the mail before she gets the okay message in (4)
– Once CF7 sent the mail (4-5?), the temporary file gets deleted from the temp folder
– I tried to watch the temp folder with standard linux tools but could not find any files being written during a test upload and form submission

What did I get right and what works differently than I think?