Compress a PDF to Send It as an Email Attachment
When a PDF won't send, you've almost always hit your mail provider's attachment cap: Gmail allows 25MB total per email, Outlook and Microsoft 365 about 20MB, and most others land somewhere between 10MB and 25MB. Go over and the message either bounces or your file is quietly swapped for a cloud link instead of the document itself. The quick fix is to shrink the PDF under the limit with compress cat's Compress PDF — drag it in, set a target a little below the cap, and click Start. It all runs locally in your browser and nothing is uploaded. Below: the real limits and how to hit them.
What are the attachment limits for each provider?
The cap applies to the whole message — every attachment plus the body — not to a single file, so packing several PDFs into one email is the fastest way to blow past it. Size against your recipient's provider, not just your own, since the smaller of the two wins.
- Gmail: 25MB total per email; over that it auto-converts the file to a Google Drive link.
- Outlook / Microsoft 365: about 20MB on the web, and the desktop client is similar by default.
- Yahoo / iCloud Mail: roughly 25MB and 20MB respectively; larger files route through Mail Drop or a link.
- Rule of thumb: aim for ~80% of the cap — receiving gateways often enforce a stricter limit than the sender's.
How do you shrink an oversized PDF enough to send?
First check how far over the limit you are. A little over and one pass is enough; a lot over — say a 40MB scanned contract that has to fit in 25MB — and you'll want a tighter target or fewer pages.
- Open Compress PDF and drag in the file you want to send (add several at once if needed).
- Set a target a little below your provider's cap — e.g. 20MB for Gmail, 15MB for Outlook — to leave room for the body.
- Click Start; compress cat binary-searches toward your target locally in your browser.
- Compare before/after, confirm it's still legible, download, and attach.
Sending several PDFs at once and going over?
Because the cap is per message, three or four files stack up fast. Two ways out: compress each one smaller, or combine them into one file and compress that.
- Compress each separately: give each a share of the cap — four files under a 20MB cap means ~4–5MB each.
- Merge then compress: use Merge PDF to combine them into one, then compress the result under the cap — one download, nothing missed.
- If it still won't fit: trim with Delete Pages, or use Split PDF to send across a couple of emails rather than forcing it.
- Skip the 'large attachment' link when you can: for anything formal, a real attachment under the cap beats making the recipient click through to download.
Frequently asked questions
Gmail says my attachment is over 25MB — how do I send the actual file, not a link?
Compress the PDF under 25MB (aim for 20MB to leave headroom) and it sends as a real attachment instead of being converted to a Google Drive link. Compression runs locally in your browser, with nothing uploaded.
I need to email several PDFs and together they're over the limit — now what?
The cap is the message total. Compress each file smaller, or use Merge PDF to combine them into one and compress that under the cap. If it still won't fit, trim pages with Delete Pages or split across a couple of emails.
Will compressing make it unreadable for the recipient?
Not if you don't overdo it. Set the target to 'just under the cap' rather than as small as possible — it only needs to send, so there's no reason to sacrifice clarity. Zoom in to check before sending.
Are my email attachments uploaded to compress cat's servers?
No. Compression runs in your browser via WebAssembly, so the PDF you're sending stays on your device and never touches a server.
Updated · compress cat team