Your client just emailed a 24MB PDF invoice with ‘Please sign and return ASAP’ — but when you click the attachment, Outlook says ‘File not found’. You check your desktop. Nothing. You open OneDrive. Still nothing. You panic-check your email again: the link points to https://1drv.ms/u/s!A… — but clicking it opens a blank browser tab. You’re not missing a setting. You’re missing *how Outlook actually talks to OneDrive*.
The Problem
Outlook doesn’t store files in OneDrive by default. It doesn’t back itself up there either. And it doesn’t auto-sync attachments unless you manually choose to save them *to* OneDrive — not just download them. This trips up finance teams sharing signed contracts, HR sending offer letters with scanned IDs, and project managers circulating updated Gantt charts. The confusion starts because Outlook shows OneDrive as an option in the Attach File dialog — but that only works if your account is properly linked *and* you use the right path. Worse: on Windows, Outlook 365 may show OneDrive under Insert > Attach File, while Outlook 2016 shows it only under Insert > Online Pictures (yes, really). On Mac, it’s buried behind a tiny cloud icon that disappears if you’ve ever clicked ‘Don’t show this again’. People assume ‘it’s connected’ because they log into Office 365 with the same Microsoft account. It’s not. Not until you tell Outlook to treat OneDrive as a trusted location — and even then, only for inserts, not backups.
The Fix
You need two separate things working: (1) inserting files from OneDrive into emails, and (2) backing up Outlook data *to* OneDrive. They’re unrelated. Let’s fix both.
How to get to OneDrive from Outlook
This means inserting files *from* your OneDrive into an email — not opening OneDrive in a browser.
In Outlook 365 (Windows): Click Message > Attach File > Browse Web Locations. If you don’t see that, go to File > Options > Mail > scroll to Messages section > click Editor Options… > Advanced > ensure Show the Browse Web Locations button in the Insert File dialog is checked. Then restart Outlook.
In Outlook 2019/2016 (Windows): Insert > Online Pictures > click the dropdown arrow next to the search bar > select OneDrive. Yes — it’s under ‘Pictures’, even for Word docs or Excel sheets. This is intentional. Microsoft moved it here in 2018 and never updated the label.
On Mac: Open a new message > click Insert > File > look for the small cloud icon (top-right of the file picker). If missing, go to Outlook > Preferences > General > uncheck then recheck Show cloud storage options in insert dialogs.
Keyboard shortcut: Alt+N, then A opens Attach File in Windows Outlook 365/2019 — but only if Browse Web Locations is enabled.
How to back up Outlook to OneDrive
Outlook does *not* auto-backup PST/OST files to OneDrive. That would break encryption and cause sync conflicts. But you *can* back up your Outlook data manually — and reliably — using Windows File History or a scheduled copy. Here’s how:
First, locate your Outlook data file. Go to File > Account Settings > Account Settings… > Data Files tab. Note the path under ‘Path’. Usually: C:\Users\[name]\AppData\Local\Microsoft\Outlook\outlook.pst (for POP/IMAP) or outlook.ost (for Exchange).
Then create a daily backup task:
- Open Task Scheduler (search ‘Task Scheduler’ in Start)
- Create Basic Task > name it ‘Outlook PST Backup’
- Trigger: Daily at 2:00 AM
- Action: Start a program → robocopy
- Arguments: "C:\Users\[name]\AppData\Local\Microsoft\Outlook" "C:\Users\[name]\OneDrive\Backups\Outlook" outlook.pst /copyall /r:1 /w:1
Yes — you must use RoboCopy. Copy-Paste fails on locked PST files. RoboCopy retries once, waits 1 second, and copies metadata. Save the backup folder *inside* your OneDrive folder — not beside it. That’s the only way OneDrive syncs it.
If That Doesn't Work
If OneDrive doesn’t appear in Outlook’s attach dialog after enabling Browse Web Locations:
- Sign out of all Microsoft accounts in Edge/Chrome, then sign back in *only* with your work account (not personal).
- In Outlook: File > Office Account > Update Options > Update Now. A silent update often fixes broken cloud integrations.
- Reset Outlook’s cached credentials: Windows Settings > Accounts > Access Work or School > remove your account > restart Outlook > re-add it.
- As last resort: Use Outlook Web App (outlook.office.com). OneDrive integration is more reliable there — click Attach > OneDrive > sign in. Then forward the email to yourself via desktop Outlook. It preserves the link.
Preventing It Next Time
Stop relying on Outlook to ‘just know’ your OneDrive. Do this once:
- Pin your OneDrive folder to Quick Access in File Explorer (right-click OneDrive folder > ‘Pin to Quick access’).
- In Outlook, set default save location for attachments: File > Options > Advanced > Save attachments to > browse and select C:\Users\[name]\OneDrive\Downloads. This won’t auto-upload, but it puts files where OneDrive watches them.
- Disable ‘AutoArchive’ for your main mailbox. It moves old items to local .pst files — which won’t sync to OneDrive. Instead, use Outlook’s built-in ‘Archive’ button (Ctrl+R) to move older mail to an online Archive folder — which *does* live in Exchange/OneDrive-connected cloud storage.
Related Settings
These settings change how OneDrive behaves inside Outlook — and most people never touch them:
Your Situation
Best Method
Why
Sending large files to clients
Use Outlook Web App + OneDrive sharing link
Desktop Outlook caps OneDrive upload at 100MB; web app allows 2GB per file
Need version history on attached contracts
Save file to OneDrive first, then insert via ‘Link to file’ (not ‘Insert as attachment’)
Creates live link — edits sync, version history stays, and recipients see ‘Open in OneDrive’
Corrupted cache folder — deleting forces fresh auth handshake on next launch
Team uses shared OneDrive folder for proposals
Map OneDrive folder as network drive (Z:) then use Insert > File > Browse
Avoids permission prompts and works offline — Outlook treats it like any local folder
Outlook crashes when attaching from OneDrive
Disable ‘Files On-Demand’ in OneDrive Settings > Sync and backup > Manage backup > turn off
Outlook can’t read placeholder files — needs full local copies
Sarah Mitchell
Sarah has 12 years of experience covering Microsoft 365 productivity tools and enterprise software workflows. She specializes in Excel automation and SharePoint integration.
