The actual limits, provider by provider
- Gmail: 25 MB per message. Larger files are converted to a Google Drive link automatically.
- Outlook.com: 20 MB, with OneDrive link sharing offered above that. Desktop Outlook connected to Exchange often enforces a stricter server policy.
- Yahoo Mail: 25 MB.
- Corporate mail servers: frequently 10 MB, sometimes 5 MB, occasionally lower.
Two details catch people out. First, these numbers cover the whole message — attachments, body, and signature images together. Second, attachments are Base64-encoded for transport, which inflates them by about a third: a 20 MB PDF travels as roughly 27 MB and bounces off a 25 MB limit.
The limit that matters is the recipient's
Your provider only decides whether the message leaves. The receiving server decides whether it arrives, and it can reject a message your outbox happily marked as sent. Bounce notifications are often delayed or silently filtered, so a "successful" send tells you very little. Staying under 10 MB avoids the whole class of problem.
Getting under the limit
1. Compress the PDF
Run it through Compress PDF and set a target of around 8 MB rather than accepting whatever a preset produces. Scanned documents typically drop 70–90%, which solves the problem outright. Documents exported from Word compress far less, because their weight is text and fonts rather than images.
2. Split it into parts
If compression cannot reach a safe size without wrecking legibility, split the document into two or three files and send them as separate messages labelled "1 of 3", "2 of 3". This is usually better than sending one crushed, unreadable attachment.
3. Send a link
For anything genuinely large — a photo-heavy report, a scanned archive — upload to cloud storage and share a link. Add an expiry date if the content is sensitive, and protect the document with a password first using Protect PDF.
Why your PDF is oversized in the first place
Nine times out of ten it is scanning. Office scanners default to 600 DPI colour, which produces roughly 3–5 MB per page for content that would be perfectly legible at 200 DPI in greyscale. Changing the scanner preset prevents the problem instead of fixing it afterwards.
The other common causes are full-page background images, embedded photos at camera resolution, and duplicated logo images repeated on every page.
Mistakes to avoid
- Zipping the PDF. PDFs are already compressed; a ZIP saves almost nothing and some corporate filters block the attachment entirely.
- Compressing until it "just fits". Encoding overhead means "just fits" often does not. Leave headroom.
- Sending several attachments separately. If they belong together, merge them, then compress the single result.
- Assuming delivery. For anything important and large, ask the recipient to confirm receipt.
Frequently Asked Questions
What is the maximum PDF size I can email?
Gmail and Yahoo allow 25 MB, Outlook.com 20 MB — but the recipient's server may cap at 10 MB or less, so target under 10 MB for reliability.
Why did my 24 MB attachment fail on Gmail's 25 MB limit?
Attachments are Base64-encoded in transit, adding roughly 33% to their size. A 24 MB file travels as about 32 MB.
Does zipping a PDF make it smaller?
Barely. PDF content is already compressed, so a ZIP typically saves a few percent while adding an extra step for the recipient.
How do I email a 100 MB PDF?
Do not attach it. Compress it first, then share a cloud link — ideally an expiring one, with the document password-protected if it is sensitive.