Every mail service has an attachment ceiling. Gmail and Outlook.com stop you at 25 MB (and Gmail counts encoding overhead, so the real limit is closer to 20 MB). Many corporate servers are stricter still, at 10 MB or even 5 MB. A scanned contract or a photo-heavy report blows past that easily.
You have two options: upload to a drive and send a link, or make the file small enough to attach. When the recipient expects a real attachment — for filing, for a case record, for someone who will not click a link — compression is the better answer.
Why you might not want a sharing link instead
A drive link avoids the size problem entirely, but it is not always the better choice. Some recipients — a government office, an older company system, someone who filters unfamiliar links as spam — will not or cannot open one. A link also depends on the file staying available and the permissions staying correct, whereas an attachment travels with the email and stays accessible in the recipient’s own inbox indefinitely. For anything that needs to be a permanent record, compressing to fit inside an actual attachment is usually the safer route even when a link would technically work.
Find out how big is too big
- Gmail: 25 MB stated, ~20 MB in practice.
- Outlook.com: 25 MB (10 MB for some older accounts).
- Microsoft 365 / Exchange: often 10 MB, set by the administrator.
- Yahoo Mail: 25 MB.
Aim comfortably below the limit, not right at it — the recipient’s server also has a limit, and the smaller of the two wins.
Steps
- Open the PDF Compressor and upload the file.
- Pick a medium level to start. For a file that is many times too large, go strong.
- Download the result and check the size against your target (for example, under 8 MB for a 10 MB server).
- If it is still too big, split the document or compress the output again.
When compression alone is not enough
- Split by recipient need. Use Split PDF to send only the pages that matter. A 60-page scan where the recipient needs pages 12–15 becomes a tiny attachment.
- Send in parts. Split a large manual into two or three PDFs and attach them to separate emails.
- Merge first, then compress. If you are attaching six separate PDFs, merge them into one and compress the single file — it is usually smaller than the six combined and tidier to receive.
- Re-scan or re-export lighter if you created the document yourself.
Will the recipient notice?
For a document that is read on screen, a medium compression pass is rarely noticeable. Text stays selectable and sharp because only images are re-encoded. If the recipient will print the file at high quality, use a lighter level and split the document to hit the size instead.
A note on security
Email is not a private channel. If the PDF contains anything sensitive — identity documents, financial details, contracts — consider adding a password with Protect PDF before sending, and share the password by a separate route such as a phone call or message. Compression and protection can both be applied to the same file; compress first, then protect.
Why attachment limits are stricter than they look
Mail servers encode attachments in a text-safe format called base64, which inflates the raw file size by roughly a third. That is why a service advertising a 25 MB limit really only accepts a file around 18–20 MB on disk, and why aiming for 70–80% of the stated limit is a safer target than aiming for the limit itself.
Corporate vs personal email in practice
A personal Gmail or Outlook.com account is usually the more forgiving option at 25 MB, but a work account behind Microsoft 365 or a company mail server is where 10 MB limits bite hardest, because the limit is set centrally by an administrator and cannot be changed from your own settings. If you regularly send large scanned documents from a work account, it is worth compressing as a habit rather than only when a message bounces — a bounced email with a client or an official body can look like carelessness even when the cause is a server setting nobody told you about. Keeping attachments under roughly 8 MB as a default sends cleanly through almost any mail system you are likely to encounter.
When the whole thread keeps bouncing
If you have already compressed the PDF and the email still bounces, check what else is in the thread. Forwarded messages carry every previous attachment along with them by default, so a chain of replies can be far heavier than the single file you are trying to send. Starting a new email instead of replying to an old thread, and attaching only the compressed PDF, often fixes a bounce that looked like a compression problem but was not.
Frequently asked questions
My PDF is 30 MB and the limit is 10 MB. Is that realistic?
Usually yes, if it is scanned. Scanned documents often compress by 80–95%. A digital PDF that is 30 MB is likely full of high-resolution photos, in which case splitting is the surer path.
Does compressing break digital signatures?
Re-saving a PDF can invalidate a cryptographic signature. If the document is digitally signed and that matters, do not compress it — split it or use a sharing link instead.
Should I zip the PDF instead?
Zipping rarely helps a PDF, because PDFs are already compressed internally. It is more likely to add a step for the recipient with little size benefit.
What if the recipient's server, not mine, is the strict one?
You cannot see their limit directly, but a bounce message usually states it. Treat 10 MB as a safe general target unless you know otherwise.
Is the tool free and private?
Yes. No account or watermark, and files are deleted from the server automatically about an hour later.