Below is an example of how to set up a rule that forwards all emails that contain the word "receipt" or "kvitto" and that have an attachment to the Mynt inbox:
Gmail
Go to mail.google.com
Click on the gear in the right corner and then on "Advanced settings".
Go to the tab "Forwarding and POP/IMAP", click on "Add a forwarding address" and add the address for the Mynt inbox. Wait for the address to be approved, which can take up to 1 minute.
Navigate to the search bar at the top of the page and type in (receipt OR kvitto) has:attachment.
Click the filter button to the right of the search bar and then click "Create filter".
Tick the "Forward it to:" option and add the address of you Mynt inbox.
Click on create filter - done!
Outlook (via the web)
Click on the gear in the right corner and then click on "Email".
Click on "Rules" and then "Add new rule".
Name the rule something educational, e.g. "Receipt rules Mynt".
Under "Add condition" add
"Subject or body includes" -> "kvitto" and "receipt"
"Has attachment"
Under "Add an action" add "Forward to" -> the address of the Mynt inbox.
Save the rule - done!