Compress email attachments
Gmail advertises 25 MB and Outlook 20 MB, but those apply after encoding. Base64 inflates every attachment by a third, so your real budget is noticeably smaller.
- Caps
- Gmail 25 MB, Outlook 20 MB, less in practice
- Adjusted
- Base64 adds 33%; targets already subtract it
- Privacy
- Attachments are never uploaded, it runs locally
Target size 18 MB
Drop images or videos here
Or click to browse, or just hit Ctrl + V to paste a screenshot
Images: JPEG / PNG / WebP / GIF / BMP · Videos: MP4 / MOV / WebM / AVI
Results
Before / after
Why 24 MB does not fit in a 25 MB mailbox
Mail protocols only carry text, so binary attachments are encoded as Base64 before transmission. The scheme turns every 3 bytes into 4 characters, which fixes the expansion at about 1.33×: and line breaks plus headers push it a little higher still.
usable source file ≈ advertised limit ÷ 1.37
Nearly every guide repeats the official number without mentioning this, which is why so many people get stuck asking why a carefully trimmed 24 MB file still will not send.
Limits and safe targets by service
| Service | Advertised limit | Keep source under |
|---|---|---|
| Gmail | 25 MB per message | 18 MB |
| Outlook.com | 25 MB | 18 MB |
| Outlook desktop (IMAP/POP) | 20 MB | 15 MB |
| Exchange Online | 35 MB default, admin can set 1–150 MB | 26 MB |
The compressor above already offers these safe values as presets, so picking your mail service sets the target for you.
Three details that catch people out
1. The cap covers the whole message
Three 9 MB files add up to 27 MB and fail together in Gmail. Rather than crushing each to 8 MB, send two emails and keep the quality.
2. Sending and receiving are separate gates
The stricter limit wins. Corporate Exchange users routinely assume they have 35 MB to play with, then bounce off a personal Gmail account on the other end, and the bounce notice can take minutes to arrive.
3. Cloud links are not free convenience
Gmail swaps oversized attachments for a Drive link automatically. Fine internally, riskier externally: the recipient needs access, and the link dies the next time you tidy up your Drive. Anything that needs to stay retrievable belongs in the message itself.
The actual workflow
- Pick your mail service above; the safe target loads automatically.
- Drop the attachment in, or paste a screenshot with Ctrl + V.
- Download the result, or grab several at once as a ZIP.
Worth repeating: the ZIP here is only a download convenience. Zipping photos and video saves almost nothing, the savings come from re-encoding, which is what the tool actually does.
Frequently asked questions
Gmail says 25 MB, so why does my 24 MB file bounce?
Because the 25 MB applies to the encoded message, not your original file. Attachments are converted to Base64 before sending, which inflates them by about 33%, and then the body and headers are added on top. To send reliably, keep the source file around 18 MB.
Is the limit per attachment or for everything combined?
Combined. Gmail counts the whole message, so three 9 MB files will be rejected together. Splitting them across separate emails works fine.
Does the recipient’s limit matter too?
Yes, and the stricter of the two wins. You may be able to send 35 MB through Exchange, but if their mailbox tops out at 20 MB the message bounces, sometimes several minutes later, long after you assumed it went through.
Gmail turns oversized attachments into a Drive link. Is that a problem?
It is convenient but has two costs: the recipient needs permission to open it, and the link breaks whenever you reorganise your Drive. For contracts and quotes that need to stay retrievable, a real attachment is safer.
Does zipping help?
Barely, for photos and video, those formats are already compressed. Zipping does help with Word, Excel and plain text. For media, re-encoding at lower quality or resolution is the only thing that moves the needle.