CompressToFit

Limit reference

Outlook file size limit

Aim for

15MB

They advertise

20MB

As of , Outlook.com caps attachments at 20MB. Exchange and Microsoft 365 limits are set per organisation and are often lower, so 15MB is the safe target.

Outlook’s own documentation

The catch

Aim for 15MB, not 20MB

Outlook.com allows 20MB, but the cap is measured after MIME encoding and corporate Exchange administrators routinely set it lower. 15MB is the number that actually sends.

If 15MB still gets rejected

Corporate Exchange servers are frequently configured well below the default. If a 15MB file bounces, your mail administrator has set a lower cap.

Fall back to 10MB

The tool

Compress a file to fit Outlook

Video, images or PDFs, already set to 15MB. Runs on your machine — nothing is uploaded.

Step 1: where are you sending it?

1Where is it going?

2Add your file

Video, images and PDFs, all compressed on your own machine. No upload, no account, no watermark, no limit on how many files.

There is also a dedicated 15MB page

Reference

Other platform limits

Every one of them dated, and the advertised number next to the one that works.

All 15 limits, and the form specifications

Background

Why the limit bites, and what to do about it

All guides