How to send large files securely: encrypt first, then share

The file is a 900 MB video, a folder of scanned contracts or a set of design files, and it is private. Email refuses it, and the usual workaround, "just put it in the cloud and send a link," quietly hands the file to anyone the link reaches.

How to send large files securely

Encrypt the file on your own computer first, upload the encrypted file to a cloud storage service, share the link with only the person who needs it, set the link to expire if the service allows it, and give the password by phone. Encrypting before you upload is the step that matters: the file is protected even if the link is forwarded or the storage account is breached.

Email attachment size limits, from each provider

Here is what each provider's own help page says today.

Two details are worth knowing. First, on work and school Google accounts the administrator sets the limits, so they can differ from 25 MB. Second, the recipient's provider has a say too. Apple warns that "the recipient's email app might have a smaller message size limit that prevents the attachment from being delivered."

Why a sharing link is not the same as a secure transfer

Every workaround above turns your file into a link. That is convenient, but the security now depends on two things: who the link opens for, and who can read the file where it is stored.

Link settings decide who gets in. Google describes its general access options plainly. "Restricted: Only people with access can open the file." "Anyone with the link: Anyone who has the link can use your file, without signing in to their Google Account" (Google). An "anyone with the link" file can be opened by whoever the link is forwarded to, pasted for or leaked to.

Gmail can create a link for you. When a personal Gmail attachment is over 25 MB, Gmail swaps it for a Drive link on its own. Check the sharing setting on that file before you hit send.

The storage provider can usually read the file. Ordinary cloud storage encrypts files, but the provider holds the keys. We look at what that means for Drive in is Google Drive private? The fix is to upload a file that is already encrypted, so the copy in the cloud is unreadable without your password.

Step 1: encrypt the file before you upload it

On a Mac, with Disk Utility (already installed). Apple suggests this for "confidential documents that you don't want others to see without your permission" (Apple).

1. Put the files in one folder.
2. Open Disk Utility and choose File > New Image > Image from Folder.
3. Select the folder, then click Open.
4. Click the Encryption pop-up menu and choose an encryption option. Set a strong password.
5. Choose an image format, such as Read-only Compressed, then click Save.

The result is a single encrypted .dmg file. It opens on a Mac. If your recipient uses Windows, use the next method instead.

On Windows or Linux, with 7-Zip. 7-Zip is free and open source, and it offers "Strong AES-256 encryption in 7z and ZIP formats" (7-Zip).

1. Install 7-Zip from its official site.
2. Right-click the file or folder and choose 7-Zip, then Add to archive.
3. Choose the 7z format.
4. Under Encryption, enter a strong password and choose AES-256.
5. Click OK.

Choose a strong password either way. Use at least 12 characters, or a short phrase of random words, and use it for this file only.

If the file is a single PDF, you can also lock the PDF itself. The steps are in how to send tax documents securely.

Step 2: upload it and share it narrowly

1. Upload the encrypted file to your cloud storage.
2. Share it with the recipient's email address, not with "anyone with the link," whenever the service allows it.
3. Set an expiration date if you can.

Which services let you set an expiry:

• OneDrive: "Set expiration date lets you set a date for the link to expire. After the date you set, the link won't work anymore." It can also require a password on the link. Both are "only available to Microsoft 365 subscribers" (Microsoft).
• Google Drive: "The expiration date feature is only available for eligible work or school accounts" (Google). On a personal account, remove access yourself once the file has been downloaded.
• iCloud Mail Drop: attachments expire on their own. Apple says "Each attachment expires after 30 days" (Apple).
• A file-sharing service with expiring links: many exist. The same rule applies. Upload the encrypted file, not the original.

Step 3: send the password a different way

Never put the password in the same email as the link, or in a follow-up email. Anyone who gets into either inbox would then have both halves. Call the recipient and read it out, or use an end-to-end encrypted messaging app. Microsoft says the same about OneDrive link passwords: "You'll need to provide this password separately to anyone you want to share the file with."

Step 4: close the door afterward

Once the recipient confirms the file opens:

1. Remove the sharing link, or delete the file from your cloud storage.
2. Delete the email with the link from your Sent folder.
3. Keep your own original somewhere encrypted.

A link you forget about is a link that keeps working.

Large videos and photos: shrink first

Video and photo collections are the most common reason files are too big. Compressing a folder before you encrypt it can bring it under a limit. 7-Zip compresses and encrypts in one step, and Disk Utility's Read-only Compressed format does the same on a Mac. Microsoft also notes that compressing a file "decreases its size, and it might decrease it enough to fit within the Outlook size limits for attachments."

Where Secria fits

The email that carries your link and its message is the part most people forget. It sits in your Sent folder, often next to everything else you have shared. In Secria Mail, every message is stored with zero-access encryption: your keys are made on your device and only reach our servers encrypted, and each message gets its own AES-256-GCM key. Encryption is post-quantum on every plan, free included, with ML-KEM-1024 and X25519 together. Tracking pixels are removed automatically and senders never see your IP address.

The free plan gives you 1 GB, 2 aliases and 3 folders, with no ads, no card and no phone number to sign up. For the step-by-step on encrypted email in other apps, see how to send an encrypted email.

FAQ

What is the most secure way to send large files? Encrypt the file on your computer with a strong password, upload the encrypted file, share the link only with the recipient's address, set it to expire if you can, and give the password by phone. The cloud copy is then unreadable without the password, even if the link travels further than you meant.

How do I send a large file securely via email? Email attachments are capped at about 20 to 25 MB, so send a link instead. Encrypt the file first, upload it, and email a link that only the recipient can open. Send the password by phone, never in the email.

Can I send a 1 GB file through Gmail? Not as an attachment. Personal Gmail caps attachments at 25 MB and turns anything bigger into a Google Drive link. Check that link's sharing setting, and encrypt the file before it goes to Drive.

Is Google Drive safe for sending private files? It is safe from strangers if you share with specific people instead of "anyone with the link." Google holds the keys to files stored in Drive, so encrypt sensitive files before you upload them.

Is a password-protected ZIP file secure? It can be, if you use AES-256 encryption and a strong password. 7-Zip offers AES-256 for both 7z and ZIP files. Send the password by phone, not in the same email as the file.

Do sharing links expire automatically? Some do. iCloud Mail Drop attachments expire after 30 days. OneDrive lets Microsoft 365 subscribers set an expiration date, and Google Drive offers it only on eligible work or school accounts. Otherwise, remove access yourself once the file is downloaded.

Big files will keep getting bigger. The email trail around them doesn't have to stay readable. If you want your mailbox sealed by default, you can get Secria for free.