Find the limit that actually applies
There are two limits, and the lower one wins. Your provider caps what you can send; the recipient’s provider caps what they can receive. A 25 MB attachment that leaves your outbox successfully can still bounce at the other end, and corporate mail systems are frequently stricter than consumer ones.
Attachments also grow in transit. Mail encodes attachments as text, which adds roughly a third to the size, so a stated 25 MB cap accommodates noticeably less than 25 MB of files. Aim comfortably below the number rather than squeezing up to it — if a send fails at 24 MB, this is why.
When the recipient matters — a client, a job application, a submission portal — ask or check before building the package. One question up front beats three failed sends, and a portal usually publishes its own limit, which may be far lower than any email cap. If it is a form rather than an email, the upload-limit guide covers that case.
Work out which files are the problem
Sort the folder by size and look at the top few entries. Attachment problems are almost always caused by two or three large items, not by the twenty small ones. Compressing the small files is effort spent on the wrong target.
Identify what the large files are. A 40 MB PDF is usually a scanned document — page images rather than text — and will compress well. A 40 MB video will not compress meaningfully and is the signal to stop thinking about attachments entirely. Photos sit between the two: individually compressible, collectively still large.
Note the total and your target. If twelve files total 60 MB against a 20 MB ceiling, you know you need roughly a third of the current size, which tells you whether compression alone can get there. Without that arithmetic you are guessing, and you will find out only after another rejected send.
Compress by file type, not everything at once
Each format needs its own treatment, and a single ZIP over all of them achieves little. Scanned PDFs respond well to Compress PDF, which reduces the page images inside. Photos respond to Compress Image. Documents and spreadsheets are small to begin with and compress further inside a ZIP.
| File type | What to use | Realistic outcome |
|---|---|---|
| Scanned PDF | Compress PDF | Often a large reduction |
| Text-based PDF | Compress PDF | Modest — it is already efficient |
| Photos (JPEG, PNG) | Compress Image | Substantial per image |
| Documents, spreadsheets, CSV | ZIP at Maximum | Good, and they were small anyway |
| Video | Neither | Use a link instead |
Check readability after compressing, not just the size. A compressed scan that has become hard to read is not a saving — it is a document you will have to send again. Open the result at the zoom level the recipient will use, and if the text has degraded, keep the larger version and solve the size problem another way. Blurry output after compression covers how to recover from going too far.
Bundle what is left into one archive
Once the individual files are as small as they sensibly get, combine them. One archive is easier for the recipient than fifteen attachments, and it survives mail clients that reorder or strip attachments. Build it with Create ZIP, which runs in your browser so the files are never uploaded anywhere.
Choose the level to match what is inside. A set of documents benefits from Maximum; a set of already-compressed photos or PDFs gains nothing, so Fast or Store only gets you a single attachment without spending minutes on compression that will not pay off. The before-and-after size tells you immediately which case you are in.
If the documents are all PDFs and the recipient wants one document rather than a folder, consider Merge PDF instead of an archive. A single merged PDF is often what “send me everything” actually means, and it saves them extracting anything at all. For PDF-specific size work, the email-size guide for PDFs goes deeper on that one format.
When to send a link instead
Some packages should not be attachments. Video, large photo sets, design source files and anything over a few tens of megabytes are better shared as a link from storage you already use. Most mail providers now offer this directly, substituting a link when an attachment exceeds the limit.
Check the permissions on the link before you send it. A link that requires an account the recipient does not have is worse than a failed attachment, because it looks like it worked. Confirm whether the audience is anyone with the link or named people only, and decide whether an expiry date is appropriate.
Be deliberate about links for confidential material. A link persists after the email is deleted and can be forwarded beyond the original recipient. For sensitive documents, a password-protected PDF sent as an attachment is sometimes the better choice — Protect PDF adds the password in your browser, and you can pass it on separately.
Check what the recipient receives
Send the package to yourself first, ideally to an address on a different provider, and open it there. This catches the two failures that are invisible from your outbox: a stripped attachment and a size rejection at the receiving end. It takes a minute and is the only real test.
Open the attachment from that test message rather than trusting the preview. Extract the archive, open a file from inside it and confirm the compressed documents are still legible. A package that arrives intact but unreadable has not solved the problem you set out to solve.
Then tell the recipient what to expect: the file count, the format, and the password if there is one. Keep the uncompressed originals until they confirm receipt — the compressed copies are for delivery, and the originals are what you will need if anything has to be rebuilt.
Bundle it into one attachmentZip the final set in your browser — nothing is uploaded.
Open Create ZIP →Frequently asked questions
Does zipping a PDF make it much smaller?
Usually not. Most PDFs already compress their contents internally, so a ZIP adds little. Compressing the PDF itself reduces the size; zipping mainly bundles files together.
Is the attachment limit always 25 MB?
No. Limits vary by provider and by the recipient’s employer, and encoding adds overhead, so the usable size is smaller than the stated cap. The receiving limit can be lower than yours.
Should I split a large file into several emails?
Avoid splitting one file into parts. Send separate documents as separate emails, or share a link. Multi-part archives often arrive incomplete or get blocked.