File uploading in Microsoft Teams for external guest users

Today I ran into an interesting question on the Microsoft Tech Community, about where documents would be stored in Microsoft Teams when they would be uploaded by an external guest user. I figured for regular Teams that would still be the associated Document Library in SharePoint, but what about Chats? So I decided to dive into the topic a bit 🙂

A guest user can always upload files in a Team, just as internal users can when they are member of a team. The guest user is added to the Members of the underlying Office 365 Group and therefore has access to the associated SharePoint teamsite which contains the Document Library where all the Team files are stored. Because he/she is an external user, a SharePoint license is not required to access SharePoint.

But that same guest user cannot upload files in Teams from OneDrive, because the user doesn’t have a OneDrive in that tenant. So the file upload dialog shows less options for an external user:


The uploaded file shows the external guest user as modified by user:


Good to see that everything is behaving as expected here!

Now for Chat it doesn’t work that way. For files attached to a Chat conversations, a folder is used in OneDrive for Business, called Microsoft Teams Chat Files. Files are uploaded into that folder and automatically shared with the person(s) you are having the Chat with. Since the external user doesn’t have a OneDrive license, the user cannot share files in a Chat. The paperclip icon just isn’t there:


Interestingly enough, that also works the other way around. When an internal user starts a chat with an external user, that file upload option is not available either. Kind of makes sense of course, but on the other hand you could expect that same folder created in the OneDrive of the internal user starting the Chat conversation, to be used for sharing a file with the external user. I guess Microsoft didn’t want to discriminate 😉 Or they took into account that external sharing settings for OneDrive sites could differ from the Team in question and that this could result in strange behaviour, makes more sense actually 🙂

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