Instead of sending files as email attachments, share a link. Everyone then works on the same file, and access can be removed at any time.
Steps
Select the file or folder: in the browser in OneDrive or SharePoint, in File Explorer or Finder via right-click › Share (OneDrive icon), or in Word, Excel and PowerPoint via Share in the top right.
Choose who gets access (link settings or gear icon): People in [company] for all colleagues, Specific people for selected people only, including external people.
Choose whether people can edit or only view.
Enter names or email addresses and click Send, or Copy link and send it yourself.
Sharing with external people
Always choose Specific people and enter the external person's email address.
The external person opens the link and confirms their address with a code sent by email. No Microsoft account is needed.
Share only what's necessary: a single file rather than a whole folder, View rather than Edit.
Review and stop sharing
Right-click the file or folder › Manage access. All people and links are listed there and can be removed.
Note: If you can't share externally, external sharing is blocked for this location. Please contact support.