Microsoft 365 Email Attachment Limit: 35 MB
Direct answer
The default Microsoft 365 message limit, the PDF size that leaves room for encoding, and the admin setting that can change it.
Why this matters: BytesPDF processes the file on your device and does not send it to a compression server. Delivery by email or portal is a separate step.
A Microsoft 365 work or school mailbox defaults to 35 MB per message. An administrator can change that limit. Encoding adds about a third to the transmitted size, so plan around the safe size below rather than the full 35 MB.
PDF Compression Core
Recompress supported PDF images locally with an adjustable quality and size trade-off.
or drag and drop PDFs here
PDF files only · Max 150MB per file · Up to 10 at a time
Limits
Microsoft 365 Limits and Safe Sizes
Use these checkpoints with the destination's current instructions. Requirements can vary by account, institution, region, document type, and workflow. BytesPDF does not verify or guarantee recipient acceptance. Page reviewed . See the browser-local processing architecture.
| Portal / Recipient | Requirement / check |
|---|---|
| Default per-message limit | 35 MB |
| Safe PDF size on disk | About 25 MB |
| Administrator setting | 1 MB to 150 MB, set by the tenant admin |
| On-premises Exchange | Usually 10 MB by default; check the server |
Trade-offs
Which Compression Mode Should You Pick?
Three modes — pick based on what the recipient needs to do with the file.
✅ Text documents
Usually the best candidates. Check the result before sending.
🟡 Scans and photographs
Expect softer detail. Compare with the original.
🟡 Digitally signed or fillable forms
A digitally signed file is not compressed, because compressing it would break the signature. Check form fields in the output before sending.
Before compressing a high-stakes document
Compression rewrites the PDF. BytesPDF rejects files containing a cryptographic signature because any rewrite would invalidate it. Keep digitally signed files and required PDF/A archival masters unchanged. Bookmarks, links, forms, annotations, accessibility tags, and color profiles are preserved where the PDF library can retain them, but always inspect the downloaded copy before filing or submitting it.
What is the email attachment limit in Microsoft 365?
Can I send a 30 MB PDF from Outlook with Microsoft 365?
Why does my limit differ from the default?
Ready to get under the limit?
Drop your file in — the compressor runs in this tab, so nothing is uploaded. The default Microsoft 365 message limit, the PDF size that leaves room for encoding, and the admin setting that can change it.
No account · No signup · No watermark · No PDF upload
Editorial review: Limits come from the BytesPDF guides linked on this page and were checked on October 15, 2026. Mail and portal rules change, so confirm the current limit on your account.
Last reviewed: . We update this page when provider guidance or tool behavior changes.
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Limits and examples are informational and may vary. Confirm the recipient's current requirements before submitting a high-stakes document. Digitally signed or archival-conformance files should be submitted in their original form.