Local processing · no upload

Compress a PDF for Outlook Attachments

Outlook rejects oversized attachments with its own error, and that limit is not Gmail’s 25 MB rule. Outlook.com’s published attachment cap is 20 MB. Microsoft 365 and Exchange organisations often set a lower one. PDF North compresses image-heavy files in this browser so you can read the new size before you press Send.

Open Compress PDF

Your file stays private. PDF North tools run in this browser tab. Following a guide and opening a tool does not upload the document.

How to do this in PDF North

Check the file size on disk. If Outlook has not refused it, and it is already well under that mailbox’s cap, do not flatten it.
If Outlook refused a scan, open Compress PDF, run Balanced, and confirm both the labelled size and that the pages are still readable.
Attach the download in Outlook. If Send still fails, split the PDF or use the OneDrive prompt instead of jumping to Maximum.

Outlook.com is 20 MB, and work accounts are often stricter

Outlook.com documents a 20 MB attachment ceiling and offers OneDrive when the file is larger. A Microsoft 365 or Exchange mailbox is set by an administrator. Many workplaces use 10 MB or 20 MB even when the desktop app looks unlimited. The message that the attachment exceeds the allowable limit is that mailbox rule, not a PDF setting. Gmail’s 25 MB ceiling is a different product — use compress for Gmail when Compose is what failed.

Encoding overhead, and when OneDrive is the better send

Outlook counts the encoded message, so a PDF that looks just under 20 MB can still bounce. Stay several megabytes under the cap you have actually hit. When Outlook offers to upload the file to OneDrive and send a link, that is often better than Maximum compression, which removes selectable text. The recipient still needs permission to open the link. PDF North does not upload the document to Microsoft or to us. You attach the download yourself.

Do not treat every Outlook send like a tiny portal

A 2 MB text report does not need flattening to survive a 20 MB mailbox. Compress photographed pages and scanner output that missed the cap. A form that prints 1 MB, 2 MB or 5 MB is not this job — use compress to 1 MB, compress to 2 MB or under 5 MB. Chat limits belong on compress for WhatsApp.

Frequently asked questions

What size PDF can I attach in Outlook?

Outlook.com’s published attachment limit is 20 MB. Work and school mailboxes are set by an administrator and are often lower. Use the error from the account you are actually sending with.

Is Outlook’s attachment limit the same as Gmail’s?

No. Gmail’s published ceiling is 25 MB. Outlook.com publishes 20 MB, and many Exchange organisations allow less than either number.

Does PDF North send my PDF to Microsoft?

No. Compression stays in this browser. Outlook receives the file only when you attach the download.

Should I compress a small text PDF just because I use Outlook?

No. Flattening removes selectable text. Compress scans and photo pages that the mailbox actually refused.

Why did Outlook reject a PDF that looked smaller than 20 MB?

Message encoding adds overhead, and a work account may enforce 10 MB or another admin cap. Split the PDF or accept the OneDrive prompt.

What if Outlook on my phone fails but the desktop app sends?

The mailbox limit still applies on both. Compress only when the server error is about size, then attach the smaller download. A phone can also run out of memory on a long render.

Related guides

These how-tos use the same local tool. The full list lives on PDF guides.

Related PDF tools

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