You attach a 20 MB PDF. Gmail's limit is 25 MB, so it should go through. It sends — and ten minutes later a "Message not delivered" bounce lands in your inbox. Or Outlook refuses the attachment outright. Or the client says "I never got it." Nothing is broken: you've run into the part of attachment limits that the help pages mention in one line, if at all.
Short answer: most email providers cap attachments at 20–25 MB, but the file gets about 33% bigger on its way out because of how email encodes attachments, and the recipient's limit counts too. So in practice, keep email attachments under roughly 15–18 MB, and under 10 MB if you don't know who's on the other end. Above that, compress the file or send a link.
Every Major App's File Size Limit in 2026
| Service | Max attachment / file size | What happens above the limit |
|---|---|---|
| Gmail (personal) | 25 MB to send, 50 MB to receive | Auto-converts to a Google Drive link |
| Outlook.com / Hotmail | 20 MB per attachment (25 MB total message) | Offers a OneDrive link instead |
| Microsoft 365 / Exchange Online | 35 MB send / 36 MB receive by default (admins can raise it to 150 MB) | Bounce or OneDrive link |
| Yahoo Mail | 25 MB | Offers a cloud link (Google Drive / Dropbox) |
| iCloud Mail | 20 MB | Mail Drop: up to 5 GB as a link that expires after 30 days |
| Proton Mail | 25 MB total attachments | Blocked; use Proton Drive link |
| Up to 2 GB when sent as a document; photos/videos sent normally are recompressed | Photos lose quality unless sent as document or HD | |
| Telegram | 2 GB (4 GB with Premium) | Blocked |
| Discord | 10 MB free, 50 MB Nitro Basic, 500 MB Nitro | Upload fails |
| Slack | 1 GB per file | Upload fails |
| Facebook Messenger | 25 MB | Upload fails |
Limits change: Discord cut its free limit from 25 MB to 10 MB in 2025, and Google has been rolling out 50 MB direct attachments for some Workspace Enterprise plans while personal Gmail stays at 25 MB. The table above reflects what each service lists as of September 2026.
Why a 20 MB File Fails Under a 25 MB Limit
1. The 33% encoding tax
Email was built to carry plain text, not binary files. So before your PDF leaves, your mail app converts it into text using Base64 encoding, which turns every 3 bytes into 4 characters. That's a 33% size increase, plus a little more for the line breaks email inserts every 76 characters.
The math most people never see:
- 15 MB file → about 20.5 MB on the wire
- 18 MB file → about 24.7 MB on the wire
- 20 MB file → about 27.4 MB on the wire ❌
So the real ceiling for raw files under a "25 MB" limit is closer to 18 MB. (If you want the full story of why Base64 inflates files, we broke it down in Base64 Encoding Explained: Why Files Get 33% Bigger.)
2. The limit is for the whole email, not each file
Three 9 MB files isn't "three files under the limit". It's 27 MB of attachments, plus encoding, plus your signature logo, plus the quoted thread of the last twelve replies with their inline images. Most providers count the total message, not the largest file.
3. The recipient's limit wins
Your Gmail can send 25 MB. If the recipient's company server accepts only 10 MB, which is common on older or tightly locked-down corporate mail servers, the message bounces on their side. A higher limit on your end doesn't override a lower one on theirs. This is also why "it worked when I sent it to myself" proves nothing.
5 Ways to Get Under the Limit (Without Ruining the File)
1. Compress the PDF
Scanned PDFs and PDFs exported with full-resolution photos are usually the biggest offenders. A 30-page scanned contract can often drop from 25 MB to 3–5 MB with no visible difference on screen, because the scanner saved each page at print resolution.
Use Compress PDF and check the result before you send: text should stay sharp, and photos only get noticeably soft on the strongest setting.
2. Resize and compress photos
A modern phone photo is 3–8 MB at 4000+ pixels wide. Nobody viewing it in an email needs more than about 2000 px. Two steps:
- Resize the image to 1600–2000 px on the long edge.
- Compress it at around 80% quality.
That typically takes a 6 MB photo down to 300–600 KB, a 90%+ reduction you won't see on screen. Ten photos go from "won't send" to under 6 MB.
3. Switch to a lighter format
Screenshots and graphics saved as PNG can be 5–10× larger than the same image as JPG or WebP. Converting PNG to JPG or to WebP is often the single biggest win for image-heavy emails. (Not sure which format fits? See our PNG vs JPG vs WebP guide.)
4. Split the file
If a PDF genuinely can't get smaller, like a high-resolution architectural drawing set, split it into two or three parts and send them as separate emails ("Part 1 of 3"). Every part stays under the limit, and the recipient can merge them back in seconds.
5. Send a link instead
Over ~25 MB after compression, stop fighting email and use Google Drive, OneDrive, iCloud Mail Drop, or WeTransfer. Just check the sharing permission. "Anyone with the link" vs "restricted" is the most common reason a link-share "doesn't open" for the recipient.
The Myth: "Just Zip It"
Zipping helps with text files, spreadsheets, and CSVs, sometimes shrinking them by 70–90%. But PDFs, JPGs, PNGs, MP4s, and DOCX files are already compressed internally, so zipping them usually saves 0–5%. You've added an extra step for the recipient and gained almost nothing. Worse, many corporate mail filters quarantine or strip .zip attachments entirely as a malware precaution.
Compress the file itself, not the container.
Quick Checklist Before You Hit Send
- ✅ Total attachments under 18 MB (under 10 MB for unknown corporate recipients)
- ✅ Photos resized to ~2000 px, not straight off the phone
- ✅ Scanned PDFs compressed
- ✅ Screenshots saved as JPG/WebP, not PNG
- ✅ Old inline images trimmed from the reply chain
- ✅ Over 25 MB? Link, don't attach
One bonus check: before sending a photo or document to someone outside your organisation, it's worth knowing what hidden metadata your files carry. Compressing or re-encoding a photo usually strips GPS data as a side effect.
FAQ
What is the maximum attachment size for Gmail in 2026? 25 MB for sending (all attachments combined) and 50 MB for receiving on personal Gmail accounts. Anything larger is automatically uploaded to Google Drive and shared as a link. Some Google Workspace Enterprise plans are getting 50 MB direct attachments.
What is the attachment size limit for Outlook? Outlook.com allows 20 MB per attachment (about 25 MB total message size). Microsoft 365 business accounts default to 35 MB outgoing / 36 MB incoming, and admins can raise that to 150 MB. Larger files are offered as OneDrive links.
Why does my email bounce even though the file is under the limit? Usually one of three reasons: Base64 encoding makes the attachment about 33% larger in transit, the limit applies to the whole message rather than each file, or the recipient's mail server has a lower limit than yours.
How do I send a file that's too large for email? Compress it first (PDFs and photos often shrink 70–90%), switch images to JPG or WebP, split large PDFs into parts, or upload to a cloud drive and send a link.
Does zipping a file make it small enough to email? Only for text-based files like CSV, TXT, or uncompressed spreadsheets. PDFs, JPGs, videos, and Office files are already compressed, so zipping them saves almost nothing, and some company email filters block ZIP attachments.
What's the WhatsApp file size limit? Documents up to 2 GB. Photos and videos sent the normal way are recompressed and lose quality, so send them as a document (or with the HD option) if quality matters.