Sharing content, such as files and folders, is a hallmark of group collaboration. An Office 365 group makes this easy by including a dedicated library, which is the primary place for storing all your group files.
When you create a file or folder in the group's library, all members of the group will be able to access it. When you add new members to the group, including guests (external users), they too will be able to access the files. Group subscribers can view and edit the files; group members can only view.
Post files to the group library
To share a file on your computer with a group, just drag it from your computer to the group's library. See Upload files to a library for more information. If the file you want to share is already in your document library, you can keep it where it is and invite the group to it.
View group files in Outlook
Sign in to Office 365, and navigate to Outlook, People, or OneDrive.
In the navigation pane, under Groups, locate the group, and then click the group name.
In the group header, click Files.
Share group files with guests
You can share group files with guests by attaching any file stored in your group library.Attach a shared file
From your group, start a conversation.
At the bottom of the conversation pane, select .
Select the source of your file: group or computer.
If you select a group as your source, select the file you want to attach.
If you select Computer as the source, select either Upload to group files or Attach as a copy. Uploading to group files enables group members to see the latest changes and co-author in real time. Attaching as a copy gives each recipient their own copy of the file for review.
Notes: When a group includes guests, you might see a message like this one informing you that attachments to guests are blocked.
Your guest will not be able to open the shared files.