When you need input on new list items from people outside the tenant, you can let a flow send an e-mail with an item description and "vote" buttons. The flow can also send the votes back to the list.
In this article Peter Kalmström, kalmstrom.com CEO and Systems Designer, shows how an e-mail input flow can be used for approvals from a legal department that not yet use SharePoint.
Each time a new project is added to a "Projects" list, and e-mail with three options is sent to the legal department automatically. The responsible person at the legal department clicks on the "Approved", "Rejected" or "Need More Info" button, and that input is sent back to a "Legal approval" column in the Projects list.
Create a blank flow and use the trigger SharePoint - when an item is created' for the Projects list.
Add the action, Office 365 Outlook, send email with options?.
Fill out the e-mail details:
Receiver e-mail address.
Subject: general text, for example,New project for approval??? + the dynamic content,Project Title?.
Fill out the options with comma between them: Approved, Rejected, Need More Info.
Add the dynamic content,Project Description? in the body.
Add the action 'SharePoint, update item? for the Projects list.
At Id, add the dynamic content,ID?.
At,Legal Approval? add the dynamic content,SelectedOption?. That will put the response from the Legal department in the SharePoint list.
Remove all the default options so that all other fields are blank.