What it does

Teams doesn't store files itself. Channel files live in SharePoint, chat files live in the sender's OneDrive, and the Files tab, attachments and sharing links are just Teams views over those two services.

Key facts

• Standard channels all share the team's SharePoint site. Each standard channel is a folder in the site's default document library, and the channel's Files tab points at that folder.
• Private channels and shared channels each get their own SharePoint site. Their Files tab points at the default document library of that channel site.
• On the team site, team owners and members are added to the site owners and members groups automatically. You can share from SharePoint, but Microsoft recommends managing access through Teams.
• Private and shared channel sites can't be shared separately — their permissions come from channel membership.
• Files in standard and private channels can be shared with sharing links across the organisation, and with guests if guest sharing is on. Files in shared channels can only be shared with org members and the channel's external participants.
• Files shared in 1:1 and group chats are uploaded to the sender's OneDrive, in a folder called Microsoft Teams Chat Files, and shared only with the people in that chat.
• Emails sent to a channel's email address are stored in an Email Messages subfolder of the channel folder.
• Recordings of non-channel meetings go to a Recordings folder in the OneDrive of the person who started recording; channel meeting recordings go to a Recordings folder in the channel's folder in SharePoint.
• Without a SharePoint licence a user has no OneDrive, can't share files in chats, and can only share files in standard channels.
• Because everything is in SharePoint and OneDrive, tenant-level retention, DLP and sharing policies for those services apply to Teams files as well.

When to use / skip

This isn't a feature you switch on — it's the architecture, and you need to understand it on every Teams deployment. The practical question is where you tell people to put things. Working documents that belong to a team go in the channel, so they live with the team and survive people leaving. Quick one-off shares belong in chat and that's fine, as long as everyone understands those files are owned by the sender's OneDrive.

Where clients get into trouble is treating chat as the filing system. Six months later the key spreadsheet is in someone's Microsoft Teams Chat Files folder, and when that person leaves, the file's fate depends on the OneDrive retention setting for leavers. Steer people towards channels for anything with a lifespan longer than the conversation.

Configuration decisions

• Org-wide and site-level external sharing settings in SharePoint — they decide what Teams users can actually share, regardless of what Teams settings say.
• Default sharing link type (specific people vs organisation) for the tenant, and whether Teams team sites should differ from the tenant default.
• OneDrive retention for departed users, given that chat files and non-channel meeting recordings sit in personal OneDrives.
• Whether to give team owners guidance on using channel folders vs separate document libraries for structured content.
• How file migrations from on-prem file shares map to teams and channels — standard channel folders vs dedicated private/shared channel sites.
• Whether SharePoint site creation and storage quotas need adjusting for teams with many private or shared channels, since each one is an extra site.

Gotchas

• Renaming a channel doesn't rename its SharePoint folder in every case — and people who go to SharePoint directly then can't find their channel. Check the current behaviour before promising anything about renames.
• Users who delete a file from the chat expecting it to vanish for everyone are often surprised; the source sits in the sender's OneDrive and that's what controls access.
• If a user has been licensed without SharePoint (it happens with custom licence assignments), chat file sharing just fails. Licence-option audits catch this.
• Moving or reorganising folders in SharePoint can break the Files tab link for a channel. Tell site owners to leave the channel folders alone.
• Private and shared channel sites don't appear as subsites of the team site — they're separate sites with their own URLs. Backup and migration tooling has to be told to pick them up.
• Guests in a team can see channel files; guests in a chat see only what's shared to that chat. Don't let anyone assume chat and channel sharing behave the same way.

Consultant notes

• Draw the storage map (team site, channel sites, sender OneDrives, recordings) for the client early. It answers half the governance questions before they're asked.
• Pull SharePoint and OneDrive admins into the Teams design — sharing posture is set on their side.
• Sync the channel library via OneDrive shortcuts rather than the old sync button for users who want files in Explorer; confirm current client behaviour before writing user guidance.
• For leavers, make the HR offboarding process include reviewing OneDrive content that was shared from chats.
• When a client asks "is it in Teams?", the honest answer is "it's in SharePoint or OneDrive" — set that expectation for backup, retention and eDiscovery conversations.

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Worth revisiting if Microsoft changes where non-channel meeting recordings are stored, or how channel folder renames are handled