mailwarden

A reliable, native Gmail MCP server — full mailbox triage for AI assistants, with the feature nobody else ships: snooze.

Highlights

• Snooze — the feature nobody else ships. Archive a thread now, have it resurface in the inbox on a date. Built on dated labels + a sweep, so it works from any client and survives restarts.

• Search you can trust. Gmail's own search index silently drops is:unread in some operator combinations — search re-verifies every hit against its live labels and discards the index's false positives. Paginated via pageToken/nextPageToken.

• Bulk operations that scale. bulk_modify archives/labels everything matching a query at 1000 messages per API request — with per-chunk partial-success reporting instead of all-or-nothing. The snooze sweep uses the same batch path.

• Structured outputs. Every tool declares an outputSchema and returns validated structuredContent alongside fenced JSON text — no parsing guesswork for clients.

• Small attack surface. No send tools (no exfiltration path for prompt-injected mail), optional read-only mode, no telemetry, no open ports by default, symlink-safe download fencing, injection-fenced output. One deliberate exception: unsubscribe / bulk_unsubscribe (manage tier) contact the opt-out endpoint named in a message's own header — the only non-Google host mailwarden ever reaches, and a read-tier deployment makes no outbound request at all. Details under Security & privacy and Unsubscribing.

• Correct with real-world mail. RFC 2047 headers decoded (=?UTF-8?B?…?= → readable text), bodies decoded in their declared charset (no mojibake for ISO-8859-1/Shift_JIS mail), 429/5xx retried with exponential backoff.

Related MCP server: Gmail MCP

Why

Connectors that sync or cache your mailbox can lag behind it — and even Gmail's own search index is sometimes loose (see below). mailwarden talks straight to the live Gmail API (no cached snapshot) and re-verifies what the index returns, so what you see is what's actually there. It's a generic Gmail capability layer — keep your own rules/logic in your AI client, not in the server.

search goes one step further than the raw API: Gmail's threads.list index is sometimes loose for read-state operators — is:unread is silently dropped in some operator combinations (e.g. category:updates is:unread -in:inbox returns read mail too). Since every hit is fetched live anyway, search re-checks the unambiguous predicates (is:unread/is:read/is:starred/in:inbox/category:…, with negation) against each thread's true labels and drops the index's false positives.

Compared to other Gmail MCP servers

Most Gmail MCP servers cover the same read/label/send surface. Two capabilities are still unique to mailwarden, and one deliberate omission is a security feature, not a gap.

Snapshot as of August 2026, from each project's public docs/repo; — = not offered / not documented. Send capability is listed as a security property: mailwarden's lack of it is intentional (see Security & privacy).

The moat isn't any single row — it's snooze + live re-verification together: an actual inbox-workflow layer that acts on the mailbox's current state, not a cached snapshot. Where competitors have caught up (bulk actions, at-rest encryption) it's noted honestly above.

Why re-verification matters — a concrete case

Ask an assistant to "archive the unread promotional mail that's already skipped my inbox" and it will reach for the obvious query, category:updates is:unread -in:inbox. Gmail's threads.list index answers loosely here: it silently drops the is:unread constraint and hands back read mail too. A server that trusts the index now archives threads you'd already read — mail you never meant to touch, gone in a bulk action you can't easily reverse.

mailwarden fetches every hit live anyway, so search re-checks the unambiguous predicates (is:unread, is:read, in:inbox, category:…, with negation) against each thread's true labels and drops the index's false positives before any tool sees them. The bulk action then runs on exactly the set you asked for. This is the difference between acting on what Gmail indexed and acting on what's actually in the mailbox right now — and it's why snooze/sweep are safe to hand to an assistant: the sweep resurfaces only threads whose snooze is genuinely due, verified against live labels at run time.

See it yourself — no Gmail account needed. From a clone of the repo (the demo is a repo-only verification script, not part of the npm package):

git clone https://github.com/csitte/mailwarden && cd mailwarden
npm install && npm run build
node scripts/demo-reverify.mjs

The demo drives the real search() against a fake Gmail API whose index is deliberately loose (returns a read thread for an is:unread query, exactly as Gmail does) and shows mailwarden dropping the false positive. It asserts the outcome, so it exits non-zero if the behavior ever regresses. The same case is locked by unit tests in test/gmail.test.ts ("drops index false positives via live-label re-verify").

Tools

All tools declare an outputSchema and return structured content (validated, machine-readable) alongside the same JSON as fenced text — clients never have to parse prose.

How snooze works (no Gmail API snooze exists — we build it)

snooze removes INBOX and applies a dated label MCP/Snoozed/<key>, where the key is either YYYY-MM-DD (due all day) or YYYY-MM-DDTHHMM (due at that local minute). The until argument takes an explicit date, a date+time (2026-06-20 9am, …T17:00), or a preset resolved server-side — today, tomorrow, weekend (next Saturday), next week (next Monday), a weekday name (monday–sunday, next occurrence), in N days, or in N hours — and a date preset may carry a trailing time (tomorrow 9am, monday 8:30), so the caller never has to compute the moment itself. sweep_snoozed finds due labels and returns those threads to the inbox (marked unread); a timed snooze wakes at the first sweep on/after its minute, so wake latency equals your sweep interval. Run the sweep:

• on demand (sweep_snoozed tool),

• via cron: mailwarden --sweep,

• or automatically: set MAILWARDEN_AUTO_SWEEP=1 (hourly sweep while the server runs).

Filters (persistent auto-triage rules)

create_filter sets up a Gmail server-side rule: mail matching the criteria automatically gets the given label actions — the mailbox keeps triaging itself with no assistant in the loop.

• Criteria: from, to, subject, query (full Gmail search syntax), negatedQuery, hasAttachment, excludeChats, and size + sizeComparison (smaller/larger, given together). At least one is required.

• Actions (label only): addLabels / removeLabels, by name or id (an unknown name in addLabels is auto-created, nested via /). Common recipes: skip the inbox → removeLabels: ["INBOX"]; auto-mark-read → removeLabels: ["UNREAD"]; auto-trash → addLabels: ["TRASH"]; star → addLabels: ["STARRED"]; never-spam → removeLabels: ["SPAM"]; file under a label → addLabels: ["Receipts"].

• Existing mail: a filter only runs on messages arriving after it's created. Pass applyToExisting: true to also apply the same actions once to mail already in the mailbox — mailwarden builds a Gmail search from the criteria and runs a bulk modify (up to maxMessages, default 1000; same loose-index caveat as bulk_modify, and the one-off pass excludes Spam/Trash). This requires at least one positive criterion (from/to/subject/query/hasAttachment:true/size): an exclusion-only rule (negatedQuery or hasAttachment:false) is refused for applyToExisting because it would match almost the whole mailbox — create such a filter without the flag. The outcome comes back under applied (the query used, matchedMessages/modifiedMessages/modifiedThreadCount counts, capped when the match set hit maxMessages, per-chunk failed, and an error string if the whole pass failed); it's null when applyToExisting was not set. The filter is created first, so a partial or failed backlog pass is reported in applied, never raised — the rule still stands.

• No forwarding — see Security & privacy.

• Requires the gmail.settings.basic scope; re-run --auth once if you authorized an older version. Not available in read-only mode.

Unsubscribing — the one outbound request

list_unsubscribe (read tier) reports what the sender offers, without contacting anyone. It reads the newest message that actually carries a List-Unsubscribe header — a reply threaded onto a newsletter sits at the end and advertises nothing, which would otherwise read as "this list has no opt-out". list_subscriptions (read tier) does the same across a whole slice, grouped by sender, so you can see who keeps writing and which of them can actually be left — one header fetch per sender rather than per thread. unsubscribe and bulk_unsubscribe (manage tier) act on it — and that is the only place mailwarden ever talks to a host that isn't Google, so the rules are tight:

• There is no URL parameter. The endpoint comes from the message's own header and nowhere else. A URL argument would let a prompt-injected mail turn the tool into an exfiltration channel (mailbox content in a query string); the header cannot carry data the model chose.

• Only RFC 8058 one-click is performed — the sender must have opted in via List-Unsubscribe-Post. A plain https: link is meant for a human in a browser and is handed back, not fetched.

• mailto: opt-outs are never performed. They would require sending mail, which mailwarden cannot do. The address is reported so you can act on it yourself.

• Fixed request, discarded response. The POST body is always List-Unsubscribe=One-Click and is never derived from anything; the response body is cancelled unread. What returns to the model is the status code and the URL actually called — no content from the endpoint, so it cannot answer with instructions. (A 301/302/303 redirect is followed as a GET, i.e. with no body at all.)

• One request per sender, sequentially, inside one budget. bulk_unsubscribe takes thread ids (never a query — a query-driven bulk would fire off a request per matched sender before anyone had looked). Threads from a sender whose request already went out are reported with duplicateOf and cost no second request: two threads from one list share an opt-out, and calling it twice only confirms your address twice. A sender is only recorded once a request actually reached an endpoint, so a refusal or a dropped connection still leaves the next thread its own try — and if the skipped thread advertises a different endpoint, the reason says so, since one sender can run several lists. Capped at 25 threads and 60 seconds per call; whatever the budget doesn't cover comes back as skippedOutOfTime rather than silently undone. None of it can be reversed, which is why all three limits exist.

• SSRF guards. https only, default port only, no credentials in the URL, and every hop — including redirects, followed at most 3 times — must resolve exclusively to globally reachable addresses. The check parses each address to its bytes and matches it against the IANA special-purpose registry, so every spelling of the same address gets the same verdict (::1 and 0:0:0:0:0:0:0:1 alike); an address that does not parse is refused. DNS resolution and all hops share one 10-second budget. Not rebinding-proof (fetch resolves again when it connects) — see SECURITY.md; what survives that gap is a blind POST whose response is never read.

Check it against your own mail before you trust it. From a repo clone (repo-only, not in the npm package), after npm run build and mailwarden --auth:

node scripts/probe-unsubscribe.mjs --vet          # category:promotions, 25 threads
node scripts/probe-unsubscribe.mjs "from:substack.com" --max 50 --vet

It prints each real List-Unsubscribe header next to what the parser made of it, and --vet also runs the endpoint through the URL vetting and the address guard — so you see both whether the parser understood the header and whether the guards would have let that opt-out through. Strictly read-only: no request is ever made to a sender, and nothing in the mailbox changes.

What it can't undo: the request tells the sender your address is live. A sender that ignores its own opt-out is beyond any client's reach — pair unsubscribe with create_filter or trash for those. Not offering an automatable option is reported as unsubscribed:false with the alternatives, not as an error. A read-only deployment gets list_unsubscribe and list_subscriptions, and never makes the request at all.

Security & privacy

For the full threat model — trust boundary, per-threat mitigations, explicit non-goals, and how to report a vulnerability — see SECURITY.md. The highlights:

• No telemetry. Nothing phones home — no analytics, no crash reporting, no tracking.

• No open ports by default. stdio only. The optional --http listener binds to 127.0.0.1 (not the LAN) and refuses to start without a MAILWARDEN_TOKEN bearer token — set MAILWARDEN_ALLOW_NO_TOKEN=1 to override on a trusted, isolated network. On a loopback bind it also validates the Host header (DNS-rebinding defense). For remote hosting, set MAILWARDEN_HOST and front it with TLS.

• No send tools — by design. mailwarden cannot compose, reply, or forward. A prompt-injected instruction inside an email has no exfiltration path through this server. create_filter follows the same rule: it can label, archive, trash, star or mark mail, but never creates a forwarding filter (which would be an exfiltration path). list_filters still surfaces any forwarding filter already on the account, so you can spot one. This holds because no such tool exists and none can be registered at runtime; for the stronger variant, where Google refuses to send rather than mailwarden declining to, see Read-only mode below.

• One outbound host, no model-chosen URL. The unsubscribe tool is the only code path that contacts a non-Google host. Its endpoint is read from the message's List-Unsubscribe header — never from a tool argument — the request body is fixed and the response body is discarded, so it cannot become a data channel. https/default-port only, redirects re-validated, and any hop resolving to a private, loopback, link-local or metadata address is refused. See Unsubscribing.

• Tool tiers (progressive disclosure + least scope). MAILWARDEN_TOOLS advertises only the tiers you name — read (the read tools), manage (mailbox mutations, snooze, downloads), filters (server-side filter CRUD, the only tier whose tools need gmail.settings.basic). Default is all three; e.g. read,manage gives a full triage surface without filter management. The OAuth scopes requested at --auth are derived from the enabled tiers — a read deployment asks only for gmail.readonly, and gmail.settings.basic is requested only when the filters tier is on. And the filter tools are hidden automatically when the stored token doesn't carry gmail.settings.basic (e.g. a token authorized before you enabled the tier) — re-run --auth to grant it. Older tokens without a recorded scope are advertised as before, with the runtime insufficient-scope message as the fallback.

• Read-only mode. Set MAILWARDEN_READONLY=1 (shorthand for MAILWARDEN_TOOLS=read) and only the read tools (search, get_thread, list_labels, list_snoozed, get_profile, triage_digest, list_unsubscribe, list_subscriptions) are registered — nothing that can change the mailbox or write files is even advertised to clients (the filter tools, which need the broader gmail.settings.basic scope, are excluded too). Recommended for shared/HTTP deployments that only triage. It is also the only tier whose no-send property Google enforces: it holds a gmail.readonly token, which Gmail's send endpoints reject outright. manage needs gmail.modify, and Gmail does accept that scope for sending — mailwarden simply exposes no tool that would. So a read deployment could not send even if this binary were replaced; a manage one cannot send because there is nothing to call. (There is no send-free write scope to switch to — see SECURITY.md, threat 1.)

• Fenced downloads. With MAILWARDEN_DOWNLOAD_DIR set, attachment writes are confined to that directory (realpath-canonicalized, symlink-aware) and never overwrite an existing file.

• Untrusted-content fencing. Every tool result is wrapped in <untrusted-tool-output> markers and stripped of invisible/BiDi-override characters, so clients can tell quoted mail content from instructions.

• Live API, no copy. No mailbox mirror or search index is stored anywhere. The only local state is your OAuth token in ~/.mailwarden/.

• Optional token encryption at rest. token.json holds a refresh token; on disk it is protected only by mode 0o600 (a no-op on Windows). Set MAILWARDEN_TOKEN_PASSPHRASE to a passphrase and the token is stored AES-256-GCM-encrypted (scrypt-derived key), so a copy of the file — a backup, a synced folder, another machine — is useless without the passphrase. Re-run mailwarden --auth once after setting it to encrypt the existing token. Note the boundary: this defends against file theft, not against malware running as your user (which can read the passphrase from the environment too).

Quick start

claude mcp add mailwarden -- npx -y mailwarden

That's the whole install — npx fetches and runs the published package, no clone or build step. You only need Google OAuth credentials once (below).

Setup

First time setting up a Google OAuth app? Follow the step-by-step setup guide — it walks through the Google Cloud Console with exact click paths, explains the "unverified app" screen, and covers the trap that makes tokens die after 7 days. The short version:

1. Google Cloud: create a project → enable the Gmail API → configure the OAuth consent screen and publish it to Production (in Testing status, Google expires refresh tokens after 7 days) → create an OAuth client ID of type Desktop app → download it as credentials.json.

2. Put credentials.json in ~/.mailwarden/ (or set MAILWARDEN_CREDENTIALS=/path/to/credentials.json).

3. Authorize once — opens a browser, stores a refresh token in ~/.mailwarden/token.json:

   npx -y mailwarden --auth

   Scopes requested: gmail.modify (read + label/archive/trash) and gmail.settings.basic (filter management only). If you authorized a version before filters existed, re-run --auth once to grant the added scope. To hold a token that Gmail itself refuses to send with, authorize with MAILWARDEN_TOOLS=read — see Read-only mode above.

4. Verify the setup any time with the built-in doctor:

   npx -y mailwarden --check

   It checks credentials.json, whether a token exists (and if it's encrypted), whether the granted scopes cover your enabled tiers, and makes one live Gmail call to prove the token still works — printing a concrete fix for anything that's wrong, and exiting non-zero if so (handy in CI/health checks). Diagnoses the common traps: no/wrong credentials file, never authorized, an encrypted token with no MAILWARDEN_TOKEN_PASSPHRASE, a missing scope, or the 7-day "Testing"-consent token expiry.

Connect

Claude Code (local stdio):

claude mcp add mailwarden -- npx -y mailwarden

Claude Desktop — add to claude_desktop_config.json:

{
  "mcpServers": {
    "mailwarden": { "command": "npx", "args": ["-y", "mailwarden"] }
  }
}

Remote (Streamable HTTP) — for a VPS / claude.ai custom connector:

# Loopback + token required by default. For real hosting, bind outward and keep the token:
MAILWARDEN_TOKEN=<secret> MAILWARDEN_HOST=0.0.0.0 npx -y mailwarden --http   # :8787/mcp

Then in claude.ai: Settings → Connectors → Add custom connector → your https://your-host/mcp URL. In Claude Code: claude mcp add --transport http mailwarden https://your-host/mcp.

Multiple accounts

One OAuth app (one credentials.json) can authorize several Gmail accounts. Each account keeps its own refresh token in a separate file, selected by MAILWARDEN_ACCOUNT:

mailwarden --auth --account work        # stores token.work.json
mailwarden --auth --account personal    # stores token.personal.json

Run them side by side by registering the server once per account, each with its own MAILWARDEN_ACCOUNT. Every instance is fully isolated — its own token, its own granted scopes, its own tool surface — so nothing can act on the wrong mailbox:

{
  "mcpServers": {
    "gmail-work":     { "command": "npx", "args": ["-y", "mailwarden"], "env": { "MAILWARDEN_ACCOUNT": "work" } },
    "gmail-personal": { "command": "npx", "args": ["-y", "mailwarden"], "env": { "MAILWARDEN_ACCOUNT": "personal" } }
  }
}

Account names are case-insensitive — they become filenames, so Work and work would be the same file on Windows/macOS. mailwarden lower-cases them (--account Work → token.work.json) so a name always maps to exactly one mailbox.

mailwarden --check shows the active account and lists the others it finds. With no MAILWARDEN_ACCOUNT set, everything uses the default token.json exactly as before — this is fully backward compatible.

From source

git clone https://github.com/csitte/mailwarden && cd mailwarden
npm install && npm run build
node dist/index.js --auth

Config (env)

Status

Working and used in daily mailbox automation. Core Gmail tools + snooze implemented against googleapis, covered by a vitest suite (458 tests — npm run coverage). Current version: see the npm badge above, the changelog, or releases. PRs welcome.

License

MIT © C.Sitte Softwaretechnik