The attachment limit you were told is not the limit you get. Email encoding inflates every attachment by roughly a third before it is sent.
What actually fits
| Provider | Stated limit | Real attachment size |
|---|---|---|
| Gmail | 25 MB | ~18 MB |
| Outlook.com | 20 MB | ~15 MB |
| Exchange (default) | 10–35 MB | Set by the administrator |
| Yahoo | 25 MB | ~18 MB |
| Many corporate servers | 10 MB | ~7 MB |
Both ends have to accept it, and the receiving limit is the one you cannot see. A file that sends successfully can still be rejected on delivery — sometimes silently, sometimes with a bounce hours later. Treat 10 MB as the practical ceiling for anything going to an address you do not control.
Getting the size down
Almost every oversized PDF is oversized for one of two reasons, and identifying which one first saves a lot of pointless compression.
Scanned pages at high DPI, and embedded photographs at full camera resolution. Text and vector content are tiny by comparison — a 200-page text document is usually under a megabyte.
- Compress it. Downsampling images typically achieves 50–80% on a scan-heavy file.
- Check the scan resolution. 600 DPI is archival; 200 DPI is fine for reading and a quarter of the size.
- Split it if only part is needed, or send in two emails.
- Share a link instead for anything over about 20 MB.
- Remove embedded fonts only as a last resort — it risks substitution.
Compress PDF runs in the browser, so a contract or a set of medical records is not uploaded to a third party on its way to being made smaller — which would rather defeat the purpose of emailing it directly.
Link or attachment
Both providers will offer to convert a large attachment into a cloud link. That is convenient and changes the properties of what you sent.
An attachment is a copy: it arrives, it stays, it works offline, and it cannot be changed or withdrawn. A link stays current, can be revoked, and gives you access data — and it breaks for external recipients whose organisation blocks the sharing domain, and for anyone reading offline.
For a signed contract or an invoice, attach the file — the recipient should hold their own copy, and permanence is the point. For a large draft under revision, link it. And for external recipients in particular, be aware that corporate mail filters strip links to consumer file-sharing services fairly aggressively.
Making links inside the PDF clickable
A link works in a PDF only if it was created as a link. Typed text that looks like an address is just text — some viewers detect and linkify it, and many do not.
The reliable approach is to create real links in the source document before exporting, and to export rather than print.
- In Word: Insert → Link, or type the address and press space, which auto-formats it into a link.
- For an email address: the target is
mailto:name@example.com. A plain address typed as text is not a link. - Add a subject line:
mailto:name@example.com?subject=Booking%20enquiry— spaces must be percent-encoded as %20. - Export, do not print. Printing to PDF converts every link to dead text.
- Test the exported file, not the source document.
That last step is worth the ten seconds. Links working in Word and dead in the PDF is the single most common version of this problem, and it is invisible unless you open the export and click one.
Documents people are meant to keep
An event schedule, a programme or a menu is a PDF that will be opened on a phone, in a venue, quite possibly with poor signal. That changes what a good one looks like.
Design for a phone screen: a single column, generous type, high contrast, and the essential information — date, time, place — on the first screen without scrolling.
- Portrait, single column. A landscape spread is unreadable on a phone.
- Body text at 12pt or larger, since it will be read at arm's length on a small screen.
- Keep it small — under 2 MB, so it opens on a weak connection.
- Make the venue address a link to a map, and the contact address a mailto link.
- Put the date in the filename. "Schedule.pdf" is unfindable in a downloads folder three weeks later.
- Add a QR code if it is also printed, pointing at a page you control so it can be updated.
The filename point is the cheapest improvement available and almost universally ignored. "Autumn-Conference-2026-09-12-Schedule.pdf" is findable months later; "Schedule (3).pdf" is not. QR Code Generator handles the printed version, and pointing it at a redirect on your own domain means a change of room or time does not invalidate everything already printed.
Frequently asked questions
What is the real email attachment size limit?
About a third less than the stated one. Attachments are base64 encoded for transmission, which inflates them by roughly 33%, so a 25 MB limit accepts a file of around 18 MB. The receiving server applies its own limit too, which you cannot see.
How do I compress a PDF for emailing?
Compress the images, which are almost always the cause — scanned pages and embedded photographs. Expect 50–80% reduction on a scan-heavy file. Check the scan resolution too: 200 DPI reads fine and is a quarter the size of 600 DPI.
Should I attach a PDF or send a link?
Attach signed contracts, invoices and anything the recipient should hold permanently. Link large drafts still under revision. Be careful with links to external recipients — corporate mail filters strip consumer file-sharing links aggressively, and links do not work offline.
How do I make an email address clickable in a PDF?
Create it as a real link in the source document with a mailto: target, then export rather than print. Typed text that looks like an address is not a link — some viewers detect it and many do not.
Why do my links stop working in the PDF?
Almost always because the file was created by printing to PDF, which converts every link to plain text. Use the application's Export or Save as PDF instead, and test the exported file rather than the source document.
How do I add a subject line to a mailto link?
Append ?subject= to the address, percent-encoding spaces as %20 — for example mailto:name@example.com?subject=Booking%20enquiry. Unencoded spaces break the link in some readers.
How should I design a PDF schedule for phones?
Portrait, single column, body text at 12pt or larger, essential details on the first screen, under 2 MB so it opens on a weak signal, and a descriptive filename including the date so it can be found weeks later.