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How to send large files securely from a Mac
By Himanshu Ranjan · Updated 8 November 2026
For people nearby, use AirDrop, whose transfers Apple says are encrypted. For email, Mail Drop handles messages up to 5 GB and keeps attachments for 30 days. For anything bigger or more sensitive, split the file into archive parts, protect them with a password, and send the password through a separate channel.
Start with who is receiving
The best method depends on distance and sensitivity. A colleague in the same room is a different case from a client on another continent. A holiday video is different from a signed contract. Choose the channel first, then shrink or split the file to fit it.
Nearby: AirDrop
Apple says AirDrop transfers are encrypted, and the recipient can accept or decline each one. In Finder, open an AirDrop window from the sidebar and drag the file onto the nearby device. On the receiving Mac, the setting is Contacts Only or Everyone. Leave it on Contacts Only when you are not expecting a file.
FileDial also has Share › AirDrop in the dial, which sends the selected file without changing it.
By email: Mail Drop and its limits
Mail Drop uploads large attachments to iCloud and sends the recipient a link instead of the file. Apple's current limits page lists a 5 GB maximum per message including all attachments, a 1 TB total across the service, a 30 day expiry per attachment, and a 30 day download window for recipients. Folders must be compressed first, attachments do not count against your iCloud storage, and a recipient's email app may enforce its own smaller limit.
Mail Drop is convenient, but remember what it is: a link on Apple's servers for up to 30 days. Anyone with the link may be able to download the file, so send a link to a sensitive file only if the file itself is protected.
Too big for any single message: split it
If a file is above the limit of your transfer service, split it into parts the recipient joins back together. FileDial's Archive › Split into 2 GB ZIP parts (WeTransfer) writes numbered .zip.001, .002 parts in a new folder. There are also Archive › Split into 1 GB ZIP parts, Archive › Split into 100 MB ZIP parts and Archive › Split into ZIP parts… for a custom size. The receiver uses Archive › Join split parts, which finds the other parts beside the first and writes the whole file. For PDFs, Organize › Split by file size… makes parts in page order, each under a size you choose.
If the goal is only to get a PDF under an email limit, Compress › Email-safe (under 20 MB) and Compress › Gmail-safe (under 25 MB) squeeze images step by step until the file fits and split it into parts if they cannot get there.
Make it private and verify it arrived intact
For a sensitive file, add a password before sending. Protect › Add password… and Archive › ZIP with password… offer Standard (ZipCrypto), which opens in Finder, and Stronger (AES-256), which needs 7-Zip or The Unarchiver. Wikipedia's ZIP article describes the original ZIP password scheme as seriously flawed, so choose AES-256 for anything that matters. Use a long passphrase and send it by phone or a different messaging app, never in the same email.
To prove the file arrived unchanged, run Batch › Checksums (SHA-256) before you send and share the checksum separately. The recipient can use Developer › Verify checksum…, which writes a report named OK or MISMATCH. Archive › Deliverable package… bundles the files with a README.txt and a SHA-256 manifest in one ZIP.
- Select the file or folder in Finder.
- Run Protect › Add password… and pick Stronger (AES-256), or Archive › ZIP with password…
- If it is still too big, split it with Archive › Split into 2 GB ZIP parts (WeTransfer).
- Send via Mail Drop or a transfer link, and send the password by another route.
Mistakes and trade-offs with large transfers
The most frequent mistake is sending the password in the same message as the file. If both travel together, the password adds nothing, because anyone who can read the email has both. Send the passphrase by phone, in person or through a different app.
The second is using a weak password method for something sensitive. The original ZIP scheme is described as seriously flawed, so choose the AES-256 option and a long passphrase made of several unrelated words. Remember that file names can reveal a lot even when contents are encrypted, so name a sensitive archive neutrally.
Third, assuming the link is private. A Mail Drop link or any transfer link can usually be forwarded, so the safeguard is the protection on the file rather than the obscurity of the link. Fourth, forgetting expiry: Mail Drop attachments expire after 30 days, so a recipient who waits a month finds nothing, and you should keep your own copy.
Fifth, splitting without testing. Before you send ZIP parts, run Archive › Join split parts on a copy yourself and confirm the whole file comes back, then compare checksums with Batch › Checksums (SHA-256) and Developer › Verify checksum… A part that is missing or renamed makes the whole transfer unusable, and finding that out after the recipient has tried is awkward.
Finally, consider whether the file can simply be smaller. A PDF full of scans compresses a lot with Compress › Compress PDF (strong), and video can be compressed before sending, which avoids splitting and shortens upload time. Local compression also avoids pushing a sensitive file through a free web tool just to shrink it.
Questions
What is the largest file Mail Drop can send?
Apple's limit is 5 GB per message including all attachments. Larger messages cannot use Mail Drop, so Apple suggests splitting the content across several messages or compressing the files first. Uncompressed folders are not accepted, so make a ZIP of any folder before attaching it.
Is Mail Drop encrypted?
Apple's Mail documentation says Mail Drop attachments are encrypted and stored in iCloud for up to 30 days. Still, treat the download link as something that could be forwarded, and put a password on the file itself if the contents are sensitive, sending that password through another channel.
How does the recipient open ZIP parts?
They put all parts in one folder and join them, for example with FileDial's Archive › Join split parts, which finds the other parts beside the one you select and writes the whole file. Without a tool that understands numbered split ZIP parts, the pieces cannot simply be opened one by one.
Is a password on a ZIP enough?
It depends on the method and the passphrase. AES-256 with a long passphrase is much stronger than the old ZipCrypto scheme, which Wikipedia calls seriously flawed. Remember the password protects the contents, and in some cases not the file names, so avoid putting secrets in the names.