June 8, 2026 · 2 min read
How to Reduce PDF File Size for Email Attachment Limits
Your PDF is 32 MB and the limit is 25. A practical, step-by-step strategy to get any document under the cap — without a paid tool in sight.
Gmail caps attachments at 25 MB. Outlook commonly at 20. Plenty of corporate mail servers and upload portals sit at 10, and government filing systems are famous for 5. Meanwhile your scanned contract weighs 32 MB and the deadline is today.
Here's the strategy, in the order that gets results fastest.
Step 1: Diagnose (10 seconds)
Try to select text in your PDF. The answer determines everything:
- Text won't select → it's a scan; every page is a photograph. Compression will work dramatically well. Continue to step 2.
- Text selects → it's born-digital; the bulk is embedded images or fonts, and page-level compression helps less. Skip to step 4.
Step 2: Compress with the right preset
Open Compress PDF, drop the file in, and pick by target:
| Situation | Preset | Typical result on scans |
|---|---|---|
| Need it a bit smaller, quality matters | Light (150 DPI) | 50–70% smaller |
| Standard email limit | Recommended (120 DPI) | 70–85% smaller |
| Tight portal limit (5 MB) | Extreme (96 DPI) | 80–90%+ smaller |
The before/after sizes are shown immediately, so you can re-run with a different preset until it fits — your original is never touched.
If the document is black-and-white paper scanned in colour (most are), flip on grayscale: colour data describing a monochrome page is pure waste, and removing it stacks with the other savings. (Need finer control? The standalone Grayscale tool has its own dials.)
The one trade-off, stated plainly: compressed pages are rebuilt as images, so text that was selectable won't be afterwards. For a scan, nothing is lost — there was never real text in it.
Step 3: Re-check against your actual limit
A subtlety that catches people: email encodes attachments in a format (base64) that inflates them ~35% in transit. A "25 MB limit" effectively means attachments up to ~18 MB. If your target is a portal upload, the stated limit is real; if it's email, aim a third under.
Step 4: When compression isn't enough (or doesn't apply)
Split the document. If the file is long, split it into parts and send two emails — crude, universal, always works. Splitting at logical boundaries ("Part 1: Agreement, Part 2: Exhibits") even looks deliberate.
Send only what's needed. Does the recipient need all 60 pages, or the 6 that changed? Extract those pages and send a file 90% smaller with better signal-to-noise.
Trim dead weight. Batch scans often carry blank backs of pages — remove them automatically. Every deleted page in a scan is real megabytes.
For born-digital PDFs: re-export from the source app with "minimum size" or "optimize for web" settings, which downsample embedded images properly at the source. Compression tools can't beat the exporter at its own game.
The 30-second recipe for the common case
Scanned document, needs to clear email: open Compress PDF → Recommended preset → grayscale on if the paper was black-and-white → compress → check it's under ~18 MB → send. Total time: under a minute, and the file never left your browser — which, for the contracts and statements that hit size limits, is exactly how it should be.
