How to shrink a video to fit outlook's 20 mb attachment limit
- Step 1Add the video — Drag in an
MP4,MOV,MKV,WebM,AVI,M4V, orTSfile, or click to browse. A lightweight<video>probe reads duration and resolution immediately so the tool can size the bitrate budget. - Step 2Set the **Target** to OUTLOOK — Open the Email provider panel and switch the
Targetdropdown from GMAIL to OUTLOOK. That sets the internal byte target to 19 MB. There is no per-MB field — OUTLOOK is the tighter of the two presets. - Step 3Check your mailbox's real limit first — Outlook.com is 20 MB, but Microsoft 365 / Exchange mailboxes can be set lower (10 MB is common). If your IT limit is below 19 MB, the OUTLOOK preset alone won't be enough — trim the clip with the lossless trimmer before compressing, or send fewer seconds.
- Step 4Run the compressor — Click Run Email Fit. JAD computes
totalKbps = 19 MB x 8 / duration, reserves 128 kbps for audio (96 kbps under 30 s), and assigns the rest to video at a 200 kbps floor. The dashboard shows whether it's on the hardware or software path. - Step 5Download the MP4 — The result card reports input → output size. Download the file, then attach it in Outlook. Because it's now under 20 MB, the desktop client sends it directly and Outlook on the web attaches it without the OneDrive prompt.
- Step 6If a corporate relay still blocks it — Some Exchange relays measure the Base64-encoded envelope (~33% larger). If a 19 MB file bounces, trim to a shorter clip and re-run, or ask whether IT can raise the per-message limit. JAD can't change a server-side policy — it can only make the file as small as the math allows.
Outlook attachment caps by account type
The 20 MB figure is Outlook.com's. Business mailboxes vary — check yours before assuming the OUTLOOK preset is enough.
| Account | Typical attachment cap | Set by | Recommended JAD target |
|---|---|---|---|
| Outlook.com (personal) | 20 MB | Microsoft default | OUTLOOK (19 MB) |
| Microsoft 365 / Exchange Online | Often 25–35 MB, but commonly lowered | Your IT admin | OUTLOOK; trim first if your cap is < 19 MB |
| On-prem Exchange (corporate) | Frequently 10 MB | Mail admin policy | Trim to shorten, then OUTLOOK — may still need a link |
| Outlook mobile app | Inherits the mailbox limit | Mailbox policy | Same as above |
OUTLOOK target — bitrate by duration
The 19 MB target is split between video and audio after the bitrate is solved from duration. The tighter cap means less video bitrate than the Gmail preset at the same length.
| Clip duration | Audio reserved | Approx. video bitrate @ 19 MB | Notes |
|---|---|---|---|
| 20 s | 96 kbps | ~7,600 kbps | Near-lossless 1080p |
| 60 s | 128 kbps | ~2,400 kbps | Clean 1080p for talking-head / screen |
| 2 min | 128 kbps | ~1,200 kbps | Good 720p-equivalent detail |
| 5 min | 128 kbps | ~400 kbps | Soft; trim or use a link for longer |
Cookbook
Outlook-specific scenarios, including the corporate cases where 19 MB still isn't small enough and the right next step is to trim rather than compress harder.
Personal Outlook.com — 1080p clip over 20 MB
A 55-second 1080p recording at 44 MB exceeded Outlook.com's 20 MB cap. The OUTLOOK preset brings it under.
Input: team-update.mp4 · 44 MB · 55 s · 1080p
Target: OUTLOOK (19 MB)
Budget: 19 MB x 8 / 55 s = ~2,890 kbps total
- 128 kbps audio
= ~2,760 kbps video
Output: team-update.mp4 · ~18.4 MB
Result: attaches in Outlook.com without a OneDrive promptCorporate mailbox capped at 10 MB
IT set the Exchange limit to 10 MB — below the 19 MB preset. Compression alone won't clear it; trim first.
Input: client-call.mov · 120 MB · 4 min Mailbox cap: 10 MB (IT policy) OUTLOOK preset -> ~19 MB -> STILL TOO BIG Fix: 1. lossless-trimmer -> keep the 45 s the client needs 2. email-compressor (OUTLOOK) on 45 s -> ~9 MB Result: clears the 10 MB corporate cap
iPhone .mov forwarded to a colleague's Outlook
An HEVC .mov from an iPhone both exceeded the cap and wouldn't preview in Outlook. The H.264 re-encode fixes both.
Input: IMG_3310.mov · 38 MB · HEVC Target: OUTLOOK -> H.264 + AAC MP4 Output: img-3310.mp4 · ~18 MB Result: under 20 MB and previews in Outlook desktop
Using OUTLOOK as a 'safe' preset for a strict Gmail relay
A 24 MB Gmail-target file bounced off a strict outbound relay that counts the Base64 envelope. The 19 MB OUTLOOK preset clears the inflated size.
Gmail target (24 MB) -> Base64 ~32 MB envelope -> relay reject OUTLOOK target (19 MB) -> Base64 ~25 MB envelope -> accepted Lesson: pick OUTLOOK when the transport, not Gmail, is the bottleneck
Large 4K source on a corporate laptop
Free tier accepts up to 1 GB, and Chrome/Edge on a corporate laptop runs the hardware path, so a big 4K capture compresses quickly and stays on-device.
Input: product-demo-4k.mp4 · 640 MB · 80 s · 2160p Tier: Free (1 GB / 1 file) -> accepted Path: WebCodecs HW H.264 (GPU) Output: ~18 MB · nothing uploaded
Edge cases and what actually happens
Your mailbox limit is below 19 MB
Provider-sideThe OUTLOOK preset targets 19 MB. If your Exchange/365 mailbox is capped lower (10 MB is common in enterprises), a 19 MB file still won't send. Trim the clip first with the lossless trimmer to shorten it, then compress — a shorter clip gets a smaller file at the same quality target.
Outlook on the web pushes a OneDrive link
By design (Outlook)Like Gmail, Outlook on the web converts oversized attachments into a cloud (OneDrive) link rather than failing outright. Compress to the OUTLOOK target (19 MB) first and it attaches the file directly instead of offering the link.
Base64 inflation trips a corporate relay
Provider-sideEmail Base64-encodes attachments, adding ~33% to the on-the-wire size. Outlook.com's 20 MB is generally the decoded size, so 19 MB is safe — but on-prem relays sometimes enforce limits on the encoded envelope. If a send bounces, trim to a shorter clip; the encoded size shrinks with it.
HEVC source won't preview in Outlook desktop
Fixed by re-encodeThe Outlook desktop client doesn't reliably preview HEVC. Because this tool always outputs H.264 MP4, an HEVC .mov/.mp4 becomes an Outlook-friendly H.264 file as part of compression — no separate conversion needed.
Output slightly over 19 MB
Soft overshootThe encoder solves for a bitrate rather than iterating to a guaranteed size, so a motion-heavy short clip can land a touch above 19 MB. It still hands you the file and logs a warning. If it edges past 20 MB, trim a few seconds and re-run.
Encode on a phone with a large source
Mobile capWithout hardware encode, the FFmpeg.wasm fallback on mobile refuses sources over 80 MB and asks you to trim or move to desktop. It also downscales anything above 720p to 720p to fit the phone's WASM heap and avoid an out-of-memory crash.
Duration can't be read
RejectedIf the probe can't determine the clip's duration, the encode throws 'Could not determine video duration' instead of guessing a bitrate. Re-export the source, or rewrap it cleanly with the transcoder first.
5-minute-plus clip looks soft at 19 MB
Quality limitAt 19 MB the video bitrate drops fast with length — around 5 minutes you're under ~400 kbps. For meeting recordings and long walkthroughs, trim to the relevant section or share a link; the tighter Outlook cap simply can't carry long footage at good quality.
Frequently asked questions
What is Outlook's attachment size limit?
Outlook.com personal accounts cap attachments at 20 MB. Microsoft 365 / Exchange business mailboxes vary and are often configured lower by IT (10 MB is common). JAD's OUTLOOK target compresses to 19 MB to stay under the 20 MB cap.
Why 19 MB and not 20 MB?
MP4 muxing and the +faststart flag add a little overhead. Targeting 19 MB leaves a 1 MB margin so the finished file can't drift back over Outlook's 20 MB ceiling.
Does anything get uploaded to OneDrive or a server?
No. The encode runs entirely in your browser. Nothing is sent to OneDrive or any JAD server — important for forwarding HR, legal, or customer recordings from a corporate device.
My corporate Outlook limit is 10 MB. Will this help?
The OUTLOOK preset targets 19 MB, which is still over a 10 MB cap. Trim the clip first with the lossless trimmer — a shorter clip produces a smaller file at the same quality target, often clearing a 10 MB limit.
Can I set a custom target like 10 MB?
No — the only control is GMAIL (24 MB) or OUTLOOK (19 MB). To hit a smaller size, shorten the clip first so the same target produces fewer megabytes, or use whatsapp-compressor (15 MB) as a smaller preset.
What format and codec do I get?
An MP4 with H.264 video and AAC audio — the format Outlook desktop, web, and mobile all preview and forward without codec issues.
Will it fix an HEVC iPhone clip that won't preview in Outlook?
Yes. The output is always H.264, so an HEVC .mov/.mp4 is re-encoded to an Outlook-friendly H.264 MP4 as part of compression.
What audio bitrate does it use?
AAC at 128 kbps for clips 30 seconds and longer, 96 kbps for shorter clips. The rest of the 19 MB budget goes to video; silent sources give all of it to video.
What input formats are accepted?
MP4, MOV, MKV, WebM, AVI, M4V, and TS. The output is always an Outlook-sized H.264 MP4.
How large a source can I drop in?
On the free tier, up to 1 GB, one file at a time — it compresses down to 19 MB. The only hard reject is on mobile without hardware encode, where FFmpeg.wasm won't take sources over 80 MB.
Why does my send still bounce even under 20 MB?
Two common causes: a mailbox cap lower than 20 MB set by IT, or a relay that measures the Base64-inflated envelope (~33% larger). Trim to a smaller clip and re-run; if it's a policy limit, only IT can raise it.
Can I automate this for repeated sends?
Yes, via the @jadapps/runner: fetch the schema from GET /api/v1/tools/email-compressor, then POST to http://127.0.0.1:9789/v1/tools/email-compressor/run. It runs locally, so the video stays on your machine.
Privacy first
Every JAD Video tool runs entirely in your browser via WebCodecs and FFmpeg (WebAssembly). Your video files never leave your device — verified by zero outbound network requests during processing.