How to Send Secure Documents to Clients, Partners, and Teams

Once you attach a financial model, legal contract, or medical record to an email and press send, you lose control over where that file goes next. The attachment sits on external mail servers indefinitely, and any recipient on the thread can forward it to an unintended address or save an unencrypted copy to a personal laptop. Standard email also struggles with file size: services such as Gmail cap attachments at 25 MB, which pushes employees to paste open cloud links into messages when sending large spreadsheets, pitch decks, or closing binders.

Sending confidential documents safely depends on four controls that email attachments cannot provide:

• Encryption in transit and at rest: Files are encrypted while moving across the network and while stored on servers.
• Scoped permissions: Access is granted at the organization, workspace, or share level rather than leaving an entire company drive exposed.
• Link and download controls: Shared links carry passwords, expiration dates, per-recipient grants, and the option to disable local downloads.
• A detailed activity log: The workspace records storage changes and system events across the organization, including uploads, edits, moves, deletions, permission changes, and share creation.

Helpful references: Fastio Workspaces, Fastio Collaboration, and Fastio AI.

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More on this subject: Security and Access Control (32 guides)

Different document handoffs call for different tools. Sending a single tax form to an accountant requires a simpler setup than running a multi-party deal room or giving an AI assistant access to project files.

1. Password-Protected Archives

Tools like 7-Zip generate AES-256 encrypted .7z or .zip archives on your local machine before you send the file. If you use this method, send the archive by one channel and deliver the password by another, such as a phone call or text message. The drawback is operational: once the recipient decrypts the archive, you cannot revoke their copy, update the file in place, or prevent them from forwarding the password.

2. Point-to-Point Transfer Services

Services such as WeTransfer and Tresorit Send replace email attachments with a download link that expires after a set window. They solve the 25 MB email attachment limit and keep large files off mail servers. However, once a recipient downloads the package to their local disk, the sender has no ongoing workspace for version updates, structured review, or signature collection.

3. Purpose-Built Shares (Send, Receive, and Exchange)

In Fastio, shares are separated by the direction of the handoff:

• Send shares: Deliver finished contracts, reports, or media packages to external recipients with optional passwords, expiration dates, and disabled downloads.
• Receive shares: Collect sensitive files from clients or vendors through a browser upload link without email attachments.
• Exchange shares: Give two sides a shared space to upload and revise files together without exposing your internal workspace.

4. Client Portals and Scoped Workspaces

For recurring client work, a branded Content Portal or a dedicated workspace gives external partners a single destination for their documents. In Fastio, external guests who open a share or portal by link do not need to create an account and do not consume a paid organization seat.

Send Confidential Documents Through Controlled Shares

Replace email attachments with password-protected shares, expiring links, client portals, and scoped workspaces for your team and AI assistants. Monthly plans start with a 14-day free trial.

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When sending confidential documents to an outside counsel, investor, or client, follow a repeatable setup so files are never exposed more broadly than intended.

1. Isolate the files in a share or dedicated workspace: In Fastio, permissions are set per organization, workspace, and share through member roles. Every member of a workspace can reach all files inside that workspace according to their role. When a recipient should only see specific files or a single folder, place those items into a dedicated share or a separate workspace rather than adding the guest to your main team workspace.
2. Grant per-recipient access or require a password: Add individual recipient grants so you can revoke one person's access later without breaking the share for everyone else. When sharing by link, enable password protection and share the password over a separate channel.
3. Set an expiration date: Attach an expiration date (such as 7 or 14 days for a proposal, financial statement, or board packet) so links close automatically once the review window ends.
4. Disable downloads for browser-only review: Turn off file downloads when recipients only need to read or review a document. Fastio renders in-browser previews for PDFs, Word documents, spreadsheets, audio, video, and design and camera formats (such as PSD, AI, RAW, and CAD files). Signed-in reviewers can leave comments anchored to a specific PDF page, image region, or video timestamp on that file version without downloading a copy.
5. Send agreements through built-in e-signature: When a document requires signing, send it for e-signature directly from the workspace. You can route signers in sequence or in parallel, require an optional one-time passcode per signer by email or text message, and have the executed PDF filed back into the workspace automatically alongside an audit certificate that records who signed, when, and from which IP address and browser.

AES-256 encryption is the current standard for protecting documents used by governments and financial institutions, with no practical attacks recorded against properly implemented AES-256. However, encryption only protects files if both the network path and the storage layer are covered.

Encryption in transit protects documents while they move between a user's browser, an API client, and the cloud server. Modern platforms use TLS 1.3, the current standard for secure connections, so intercepted network traffic cannot be read.

Encryption at rest protects files while they sit on storage disks. Fastio encrypts stored files at rest and in transit and runs on cloud infrastructure partners, including Google Cloud Platform and Cloudflare, that are certified to industry-leading security standards.

Because the files stay in a workspace rather than a locally encrypted archive, your team keeps capabilities archive encryption cannot offer:

• Per-file version history and advisory file locks: Every file keeps its full version history so prior versions can be restored at any time. When people or agents coordinate edits in a workspace or share, they can acquire an advisory per-file lock, renew it by heartbeat, and release it when finished (with override available to anyone holding write permission).
• Structured extraction with Metadata Views: When a team collects dozens of signed agreements or invoices through a Receive share, Metadata Views can extract typed fields such as effective dates, counterparties, policy limits, or invoice totals into a sortable, filterable grid without manual data entry.
• Detailed activity log: Fastio maintains a detailed activity log of what changed across the organization and who changed it, covering both human members and AI agents. The log records uploads, edits, moves, deletions, membership and permission updates, and share creation.

For most small and mid-sized companies, the hardest part of document security is scoping access across existing cloud drives and AI tools without reorganizing years of folders.

Syncing Specific Folders Without Migrating Your Drive

Most organizations store their records in SharePoint, Google Drive, Box, or Dropbox, where internal folders often mix confidential executive files with documents that external partners or AI tools need to read. Restructuring those source drives is rarely practical.

With Fastio Cloud Sync, an IT administrator or team lead can connect specific folders from Google Drive, Dropbox, Box, and OneDrive (including SharePoint document libraries through OneDrive for Business) to a Fastio workspace, one-way or two-way, on a recurring schedule or on demand. A one-way scheduled sync brings only the selected folders into the workspace while leaving the source drive untouched.

Scoping File Access for Claude, ChatGPT, and Coding Agents

Connecting an AI assistant directly to an entire SharePoint site or Google Drive often exposes far more than a project requires because user-level drive permissions are wide. Placing only the target files into a dedicated Fastio workspace solves the scoping problem before the AI ever connects.

Fastio hosts a remote MCP server with a consolidated MCP toolset at per-client endpoints (https://mcp.fast.io/mcp/tools for Claude and general MCP clients, https://mcp.fast.io/mcp/operations or the Fastio plugin for ChatGPT and Codex, and https://mcp.fast.io/mcp/code for coding agents such as Claude Code and Cursor; see https://mcp.fast.io/docs for setup steps). During OAuth sign-in, a Review Permissions screen lets you choose Read Only or Read & Write access and pick the exact organizations and workspaces the assistant can reach. With Read Only selected, write tools are not offered to the assistant.

When an AI agent builds an organization on a client's behalf, it can hand the organization to a human at the client using ownership transfer and a claim link once the setup is complete.

If a shared link is forwarded to the wrong person or an external contractor leaves a project, having your files in a controlled share or workspace lets you cut off access immediately.

Immediate containment (first 15 minutes):

1. Revoke the share or recipient grant: Open the share settings and revoke the individual recipient's access or disable the share link entirely.
2. Revoke connected agent or device sessions: If a scoped API key or MCP client connection was exposed, revoke the API key or open Settings, then Devices & Agents, then Connected Devices in Fastio and select Revoke.
3. Disable downloads on remaining shares: If related shares are still active for other parties, switch them to view-only in the browser with downloads turned off.

Review and recovery (first 24 hours):

1. Check the detailed activity log: Inspect the organization's detailed activity log to see all recorded changes during the exposure window, including any file uploads, edits, moves, deletions, permission changes, or newly created shares.
2. Restore affected files from version history: If a collaborator or agent modified or overwrote a file in an Exchange share or workspace before access was revoked, restore the previous version from per-file version history.
3. Issue a new scoped share: If the intended recipient still needs the files, create a fresh share with a new password, a short expiration date, and per-recipient access.