"File exceeds the maximum attachment size." Every provider has a ceiling, and scanned PDFs hit it constantly — a 300-dpi color scan runs 1–3 MB per page, so a 30-page scan easily lands north of 40 MB.
The limits, current as of 2026
| Provider | Sending limit | Notes |
|---|---|---|
| Gmail | 25 MB | Larger files auto-convert to a Google Drive link |
| Outlook / Microsoft 365 | 20 MB | Exchange servers often cap lower (10 MB is common) |
| iCloud Mail | 20 MB | Mail Drop links up to 5 GB |
| Yahoo Mail | 25 MB | |
| Corporate mail servers | often 10 MB | The real-world bottleneck — receiving servers reject, too |
Two traps worth knowing: attachments are base64-encoded in transit, which inflates them — by more than the "33 %" usually quoted (the arithmetic is below) — and the recipient's server can reject what yours allowed. If a document matters, staying under 10 MB per message is the only safe assumption.
The arithmetic nobody shows you
SMTP was designed for 7-bit text, so binary attachments are converted to base64: every 3 bytes become 4 ASCII characters, a 4/3 expansion. MIME then wraps that text at 76 characters per line, and each line ends in a 2-byte CRLF, so every 76 characters of payload costs 78 bytes on the wire:
4/3 × 78/76 = 1.368 → +36.8 %
Run a mail limit backwards through that factor and you get the largest file that actually fits:
| Stated limit | Largest attachment that fits |
|---|---|
| 10 MB | ≈ 7.3 MB |
| 20 MB (Outlook, iCloud) | ≈ 14.6 MB |
| 25 MB (Gmail, Yahoo) | ≈ 18.3 MB |
Subtract a little more for the message body and headers. This is why a 20 MB PDF fails on Gmail even though "20 is less than 25."
Option 1: Split the PDF into parts by size
The most reliable fix, because it needs nothing from your recipient — no Drive permissions, no expiring links, no "please request access."
- Drop the PDF on Split PDF by Size.
- Pick the recipient's limit — 25 MB for Gmail, 20 MB for Outlook, 10 MB if it's a corporate address you don't control — and leave Sending by email ticked so the tool targets the encoded size from the table above.
- Download the ZIP, then attach one part per message, labelled "Part 1 of 3" in the subject line. Part files are named with their page ranges, so the recipient can reassemble the order at a glance.
Why a dedicated tool instead of "every N pages"? Page weights are wildly uneven — a full-bleed scan can be 50× a text page — and parts don't add up to the original, because fonts and images shared across pages get stored once per part. The size splitter builds each candidate part and measures its real size, so every part is guaranteed to fit. (The standard splitter's Every N pages mode still works if you'd rather iterate by hand.)
Option 2: Send only the pages that matter
Attachment bloat is often unnecessary pages, not an unavoidably big document. Does the recipient need the whole 90-page agreement, or the signature page and two exhibits? Extract just those pages and you're usually under any limit in one message.
Option 3: A link instead of an attachment
Drive, Dropbox, and Mail Drop links bypass limits entirely — at the cost of new failure modes: permissions, expiry, corporate link-blocking, and the document living on a third-party server. For sensitive files, a split attachment keeps the document inside the mail system your organization already trusts.
Why not just compress it?
ZIP compression barely touches scanned PDFs — the images inside are already JPEG-compressed, so zipping typically saves single-digit percentages. Recompressing the images does shrink the file but visibly degrades quality and re-renders the document. Splitting keeps every page at original quality; it just changes how the pages are packaged.
The splitter runs entirely in your browser, so even that confidential 45 MB scan never touches a server on its way to becoming three attachable parts.