Instead of manually uploading your supplier's email invoice, or manually forwarding them as you receive them, you can set an auto-forwarding rule using the “from” email, in our example the supplier's email is ‘firstname.lastname@example.org’ “to” your submission email address instead.
To find your submission email (which looks something like email@example.com), go to Settings > General, and it's under Change your Email Address PIN. Yes you can change your submission email, here's how to do that.
This works where if you know your vendor always email you invoices from 'firstname.lastname@example.org', you can set this rule for them.
Here’s an example using Gmail: