You tried to send the PDF through Outlook. Got an error about size. Either Outlook.com's 20MB limit or your company's stricter cap is in the way.
What's actually going wrong
Outlook.com (consumer) caps at 20MB. Microsoft 365 corporate often allows up to 150MB outgoing, but the recipient's server may reject larger files. Many corporate servers cap at 10MB. Effective limit is usually 20MB or below.
Files above the limit get rejected outright or auto-redirected to OneDrive.
The quick fix
Compress PDF in Flint. Most files shrink to well under 20MB. Re-attach and Outlook accepts.
For very large PDFs, OneDrive sharing is the alternative — Outlook automatically offers this for oversized attachments.
If that didn't work
Corporate environments sometimes block PDFs above small limits regardless of provider capability. If compression doesn't help and you suspect a corporate filter, check with IT.
For PDFs that must stay whole, share via cloud (OneDrive, SharePoint) and email the link. Works for any size.
Prevent it next time
Know your effective limit. Compress as standard practice. And maintain cloud storage for the occasional huge file.
FAQ
What's Outlook's exact size limit?
Outlook.com: 20MB. Microsoft 365: up to 150MB outgoing, but recipient servers vary. Corporate servers commonly 10-25MB. Aim under 20MB for safety.
Why is corporate Outlook more restrictive?
IT policies set limits to control mail server load and spam vectors. Strict limits are common in regulated industries.
Does OneDrive sharing work for external recipients?
Yes if sharing permissions allow. Set the link to 'anyone with the link' for users outside your organisation.
Will compression always help?
For PDFs with images, almost always 60-90% reduction. For pure-text PDFs that are large for non-image reasons, less. Most PDFs above 10MB benefit substantially.
Outlook caps clear easily with Flint's compressor. Send real attachments, not links.