Microsoft still caps Outlook desktop to 20MB by default while Outlook.com tops out at 25MB. Use the workflow and calculators below to land just under the ceiling without sacrificing clarity.
Outlook desktop: 20MB default send limit (often enforced by Exchange admins). Outlook.com: 25MB per message before OneDrive takes over.
Need a fast fix? Jump straight to the 20MB Outlook preset or the 25MB Outlook.com preset, then verify bitrate with the calculator below.
| Scenario | Send limit | Notes |
|---|---|---|
| Outlook for Windows/Mac | 20MB default (send + receive) | Exchange admins can raise to 35-150MB, but most orgs keep 20MB to avoid bandwidth spikes. |
| Outlook.com / Hotmail | 25MB per message | Anything bigger prompts an automatic OneDrive upload with a shareable link. |
| Microsoft 365 Exchange Online | 10MB to 25MB typical | Tenant-wide transport rules or connectors may lower the threshold. Check with IT before sending 20MB+. |
| Outlook mobile apps | Mirrors server policy | Files still route through Exchange/Outlook.com, so the same 20-25MB ceiling applies. |
Compare with other providers in the email attachment limit overview.
FitToMB targets the exact encoded size you need. Pick a preset, upload your video (up to 500MB), and download a clean MP4 that sits comfortably under the Exchange cap.
Exchange Online throttles mailboxes sending many near-limit files back-to-back. Queue big videos overnight or share a single OneDrive folder for teams.
Enter the clip length to see the maximum video bitrate that keeps you under the cap. Use the quick toggles to jump between the 20MB desktop limit and the 25MB Outlook.com ceiling.
Outlook encodes every attachment before it leaves your outbox. The process adds roughly 33% to the on-disk file size. A 19MB MP4 expands to ~25MB during transport, and Exchange evaluates that inflated size against policy.
Need more room? Compress to 20MB, then attach the larger master from OneDrive so viewers can stream or download the full-quality version.
OneDrive links carry the same branding as an attachment while bypassing legacy caps. Outlook automatically uploads the file and inserts permission-aware links.
Add a quick sentence in your email body that OneDrive auto-expired links can be extended in the sharing panel. It prevents confusion when recipients revisit later.
Because Outlook desktop still enforces a 20MB Exchange default. After base64 overhead, a 24MB MP4 becomes ~32MB, so it is rejected. Compress to 18-19MB or share a OneDrive link.
No. Outlook sends files as-is until they exceed policy. Use FitToMB to control the bitrate instead of relying on unpredictable email-side compression.
Plan for roughly 33% overhead. For a 20MB limit, aim for an exported file around 18MB. The calculator above bakes in that math for you.
Switch whenever the encoded file would exceed 20-25MB or when you need shared editing/versioning. Outlook inserts a permission-aware OneDrive link automatically.