Email (IMAP/SMTP)

mcp-server-email

Multi-account email server for the Model Context Protocol. Gives LLMs full email access — read, send, search, organize — over IMAP/SMTP with connection pooling, rate limiting, and retry. Designed as the remote-email counterpart to apple-bridge (local Mail.app access).

Quick Start

1. Install

   go install github.com/boutquin/mcp-server-email/cmd/mcp-server-email@latest
   

2. Create a config file (~/.config/mcp-email/accounts.json)

   For well-known providers (Gmail, Outlook, Yahoo, iCloud, Fastmail, Zoho), host and port are auto-detected from the email domain — just provide credentials:

   [
     {
       "id": "hello",
       "email": "hello@gmail.com",
       "username": "hello@gmail.com",
       "password": "app-password-here"
     }
   ]
   

   For custom mail servers, specify host and port explicitly:

   [
     {
       "id": "work",
       "email": "hello@example.com",
       "imap_host": "mail.example.com",
       "imap_port": 993,
       "smtp_host": "mail.example.com",
       "smtp_port": 465,
       "username": "hello@example.com",
       "password": "app-password-here"
     }
   ]
   

   chmod 600 ~/.config/mcp-email/accounts.json
   

3. Add to Claude Code (~/.claude.json)

   {
     "mcpServers": {
       "email": {
         "command": "mcp-server-email",
         "env": {
           "EMAIL_CONFIG_FILE": "~/.config/mcp-email/accounts.json"
         }
       }
     }
   }
   

4. Restart Claude Code — the email_* tools are now available.

Installation

Go Install (recommended for Go developers)

go install github.com/boutquin/mcp-server-email/cmd/mcp-server-email@latest

Homebrew (macOS/Linux)

brew install boutquin/tap/mcp-server-email

Binary Download

Download pre-built binaries for your platform from GitHub Releases.

Available for: Linux (amd64, arm64), macOS (amd64, arm64), Windows (amd64, arm64).

Docker

docker run --rm \
  -e EMAIL_ACCOUNTS='[{"id":"main","email":"user@example.com","imap_host":"mail.example.com","imap_port":993,"smtp_host":"mail.example.com","smtp_port":465,"username":"user@example.com","password":"app-password"}]' \
  ghcr.io/boutquin/mcp-server-email:latest

MCP Bundle (Claude Desktop)

Download the .mcpb file from Releases and open in Claude Desktop.

Build from source

git clone https://github.com/boutquin/mcp-server-email.git
cd mcp-server-email
go build -o mcp-server-email ./cmd/mcp-server-email

Configuration

Accounts are loaded once at startup. Changes require a server restart.

Config file vs environment variable

Approach	Best for
EMAIL_CONFIG_FILE — path to a JSON file	Production use. File can be permission-locked (chmod 600)
EMAIL_ACCOUNTS — inline JSON in env var	Testing, CI, or containerized deployments

If both are set, EMAIL_ACCOUNTS takes precedence.

Account JSON schema

[
  {
    "id": "hello",
    "email": "hello@example.com",
    "imap_host": "mail.example.com",
    "imap_port": 993,
    "smtp_host": "mail.example.com",
    "smtp_port": 465,
    "username": "hello@example.com",
    "password": "app-password-here"
  }
]

Field	Required	Description
id	Yes	Unique account identifier
email	Yes	Email address
imap_host	No*	IMAP server hostname
imap_port	No*	IMAP port (993 = implicit TLS, 143 = STARTTLS)
smtp_host	No*	SMTP server hostname
smtp_port	No*	SMTP port (465 = implicit TLS, 587 = STARTTLS)
username	Yes	Login username
password	Yes**	App password or account password
use_starttls	No	Override TLS auto-detection (true/false)
insecure_skip_verify	No	Skip TLS certificate verification (dev/testing)
auth_method	No	"password" (default) or "oauth2"
oauth_client_id	No	OAuth2 client ID (required when auth_method is "oauth2")
oauth_client_secret	No	OAuth2 client secret
oauth_token_file	No	Override token file path

*Host and port are auto-detected for well-known providers (see below). Required for custom servers. **Not required when using OAuth2 authentication.

Provider auto-detection

When imap_host/smtp_host are omitted, the server detects settings from the email domain:

Provider	Domains	IMAP	SMTP
Gmail	gmail.com, googlemail.com	imap.gmail.com:993	smtp.gmail.com:587
Outlook	outlook.com, hotmail.com, live.com	outlook.office365.com:993	smtp.office365.com:587
Yahoo	yahoo.com	imap.mail.yahoo.com:993	smtp.mail.yahoo.com:587
iCloud	icloud.com, me.com, mac.com	imap.mail.me.com:993	smtp.mail.me.com:587
Fastmail	fastmail.com, fastmail.fm	imap.fastmail.com:993	smtp.fastmail.com:587
Zoho	zoho.com, zohomail.com	imap.zoho.com:993	smtp.zoho.com:587

Explicit host/port in the config always takes precedence over auto-detection.

TLS modes

TLS mode is auto-detected from port:

Port	Protocol	Mode
993	IMAP	Implicit TLS
143	IMAP	STARTTLS
465	SMTP	Implicit TLS
587	SMTP	STARTTLS

Override with "use_starttls": true or "use_starttls": false in the account object. Omit for auto-detection (recommended).

OAuth2 authentication

For providers that support it (Gmail, Outlook), you can use OAuth2 instead of app passwords. This uses the device code flow (RFC 8628) — no browser redirect needed.

1. Create OAuth2 credentials in the provider's developer console (Google Cloud Console or Azure AD)

2. Configure the account with auth_method: "oauth2":

   [
     {
       "id": "gmail",
       "email": "user@gmail.com",
       "username": "user@gmail.com",
       "auth_method": "oauth2",
       "oauth_client_id": "your-client-id.apps.googleusercontent.com",
       "oauth_client_secret": "your-client-secret"
     }
   ]
   

3. On first connection, the server initiates the device code flow — printing a verification URL and code to stderr. Visit the URL and enter the code to authorize.

4. Tokens are persisted in ~/.config/mcp-email/tokens/ and automatically refreshed. Subsequent connections reuse the stored token without re-authorization.

Supported OAuth2 providers: Gmail (gmail.com, googlemail.com) and Outlook (outlook.com, hotmail.com, live.com).

Environment variables

Variable	Required	Default	Description
EMAIL_CONFIG_FILE	Yes*	—	Path to JSON config file
EMAIL_ACCOUNTS	Yes*	—	JSON array of account configs (inline)
EMAIL_DEFAULT_ACCOUNT	No	First account	Default account ID
EMAIL_IMAP_TIMEOUT_MS	No	30000	IMAP operation timeout (ms)
EMAIL_SMTP_TIMEOUT_MS	No	30000	SMTP operation timeout (ms)
EMAIL_IMAP_RATE_LIMIT	No	60	IMAP requests/minute/account
EMAIL_SMTP_RATE_LIMIT	No	100	SMTP sends/hour/account
MAX_ATTACHMENT_SIZE_MB	No	18	Max size per attachment (MB)
MAX_TOTAL_ATTACHMENT_SIZE_MB	No	18	Max total attachment size per message (MB)
MAX_DOWNLOAD_SIZE_MB	No	25	Max attachment download size (MB)
EMAIL_POOL_CLOSE_TIMEOUT_MS	No	5000	Pool close timeout (ms)
EMAIL_DEBUG	No	false	Debug logging to stderr
LOG_LEVEL	No	info	Log level: debug, info, warn, error
LOG_FORMAT	No	json	Log format: json or text

*One of EMAIL_CONFIG_FILE or EMAIL_ACCOUNTS is required.

Config file permissions

The config file contains account passwords. Always restrict access:

chmod 600 ~/.config/mcp-email/accounts.json

Tools (22)

Account & folder tools

Tool	Description	Key params
email_accounts	List configured accounts with connection status	—
email_folders	List all folders with unread/total counts	account?
email_folder_create	Create new folder	name, account?

Message listing

Tool	Description	Key params
email_list	List messages in folder	folder?, limit?, offset?, includeBody?, account?
email_unread	List unread messages	folder?, limit?, includeBody?, account?
email_search	Search subject and body	query, from?, to?, since?, before?, folder?, limit?, includeBody?, account?

Message operations

Tool	Description	Key params
email_get	Get full message by ID	id
email_read_body	Read email body with pagination	id, offset?, limit?, format?
email_move	Move message to folder	id, destination
email_copy	Copy message to folder	id, destination
email_delete	Delete message (trash or permanent expunge)	id, permanent?
email_mark_read	Mark as read/unread	id, read
email_flag	Flag/unflag message	id, flagged
email_reply	Reply to a message (sets In-Reply-To, References, quotes body)	id, body, all?, cc?, bcc?, isHtml?, account?
email_forward	Forward a message (re-attaches original attachments)	id, to, body?, cc?, bcc?, isHtml?, account?
email_batch	Batch operations on multiple messages	action, ids, destination?, permanent?, read?, flagged?

Attachments & threads

Tool	Description	Key params
email_attachment_list	List attachments on a message	id
email_attachment_get	Download attachment by index	id, index, saveTo?
email_thread	Get conversation thread (searches across INBOX, Sent, Archive, and All Mail)	id

Send & drafts

Tool	Description	Key params
email_send	Send via SMTP with optional attachments	to, subject, body, cc?, bcc?, replyTo?, isHtml?, attachments?, account?
email_draft_create	Save draft with optional attachments	to?, subject?, body?, cc?, bcc?, isHtml?, attachments?, account?
email_draft_send	Send existing draft	id

All optional account params default to the configured default account.

Search

email_search searches both subject and body using IMAP SEARCH OR (SUBJECT "q") (BODY "q").

Optional filters narrow the candidate set server-side before body scanning:

Filter	Format	Example
from	Email address or name	"alice@example.com"
to	Email address or name	"bob@example.com"
since	YYYY-MM-DD	"2026-01-01"
before	YYYY-MM-DD	"2026-02-01"

The existing operation timeout (default 30s) prevents hung body searches on large mailboxes.

Attachments

email_send and email_draft_create accept an attachments parameter — an array of file references on the server host:

{
  "attachments": [
    {"path": "/tmp/report.pdf"},
    {"path": "/tmp/data.csv", "filename": "Q1-data.csv", "content_type": "text/csv"}
  ]
}

Parameter	Required	Description
path	Yes	Absolute file path on the server host
filename	No	Override display filename (defaults to basename of path)
content_type	No	MIME type (auto-detected from file extension if omitted)

Limits (defaults): 18 MB per file, 18 MB total (pre-base64 encoding; stays under 25 MB SMTP cap after encoding). Configurable via MAX_ATTACHMENT_SIZE_MB and MAX_TOTAL_ATTACHMENT_SIZE_MB environment variables.

Download limit: Attachment downloads (email_attachment_get) are capped at 25 MB by default, configurable via MAX_DOWNLOAD_SIZE_MB.

Validation failures (missing file, non-absolute path, size exceeded) return INVALID_ARGUMENT.

Message IDs

Message IDs are composite strings encoding account, mailbox, and UID:

{account}:{mailbox}:{uid}

Example: hello:INBOX:12345

All CRUD tools (email_get, email_move, email_copy, email_delete, email_mark_read, email_flag, email_draft_send) extract the account and folder from the ID — no separate params needed.

Error Codes

All errors are returned as MCP tool errors with a structured code prefix:

Code	Meaning
AUTH_FAILED	IMAP/SMTP authentication failed
CONNECTION_FAILED	Cannot connect to server
ACCOUNT_NOT_FOUND	Unknown account ID
FOLDER_NOT_FOUND	Mailbox doesn't exist
MESSAGE_NOT_FOUND	UID not found in mailbox
INVALID_ARGUMENT	Missing/invalid parameter (including attachment validation)
TIMEOUT	Operation timed out
INTERNAL	Unexpected server error

Resources

URI	Description
email://status	Server version, account connection state, rate limit configuration

Comparison with apple-bridge

This server and apple-bridge share an Email model and parameter semantics (limit, includeBody, folder, query) so LLMs can work with both interchangeably. Key differences:

Aspect	mcp-server-email	apple-bridge
Transport	IMAP/SMTP (remote)	Mail.app (local)
Tool prefix	email_*	mail_*
Message ID	{account}:{mailbox}:{uid}	RFC 5322 Message-ID
Folder create	Supported	Not supported (Mail.app requires UI)
Copy message	Supported	Not supported
Draft send	Supported	Not supported (Mail.app uses compose UI)
Attachments (send)	File path on server host	Not yet supported

Development

Prerequisites

• Go 1.24+
• golangci-lint
• Docker (for integration tests only)

Build

go build ./...

Unit tests

make test
# or: go test -race -count=1 ./...

Unit tests use mock implementations of the imap.Operations and smtp.Operations interfaces — no live mail server needed.

Benchmarks

go test -bench=. -benchmem ./...

Benchmark	Package	What it measures
BenchmarkPoolGetRelease	imap	Connection pool acquire/release cycle
BenchmarkExtractAttachments	imap	MIME attachment extraction
BenchmarkHtmlToText	tools	HTML-to-plain-text conversion
BenchmarkLimiterAllow	retry	Rate limiter (sequential)
BenchmarkLimiterAllow_Parallel	retry	Rate limiter (concurrent)

Fuzz testing

Fuzz targets ship with seed corpora in testdata/fuzz/ directories. Run a specific target:

go test -fuzz=FuzzParseMessageID ./internal/models/ -fuzztime=30s

Target	Package	What it fuzzes
FuzzBuildSearchCriteria	imap	IMAP search query builder
FuzzExtractAttachmentByIndex	imap	Attachment index boundary handling
FuzzExtractContentType	imap	MIME content-type parser
FuzzParseMessageID	models	Composite message ID codec
FuzzHtmlToText	tools	HTML-to-text sanitizer
FuzzSplitAddresses	tools	Email address list splitter

Lint

make lint
# or: golangci-lint run ./...

Integration tests

Integration tests exercise the full IMAP/SMTP stack against a real mail server. They are isolated behind the integration build tag and never run during go test ./....

Mail server: Greenmail

Tests use Greenmail, a lightweight Java mail server packaged as a Docker image. Key details that affect how you run it:

Setting	Value	Why it matters
IMAPS port	3993	Greenmail's SSL IMAP port (not 993). The code auto-detects TLS from port number, so tests explicitly set UseStartTLS=false to force implicit TLS on this non-standard port.
SMTPS port	3465	Greenmail's SSL SMTP port (not 465). Same UseStartTLS=false override.
Bind address	0.0.0.0	Greenmail defaults to 127.0.0.1 inside the container, which makes Docker port-mapping silently fail (connections get EOF). You must pass -Dgreenmail.hostname=0.0.0.0.
Username	test	Greenmail uses the local part only (before @) as the login username — not the full email address. If the user is test@example.com, the IMAP/SMTP username is test.
TLS certificates	Self-signed	Greenmail generates self-signed certs. Tests set InsecureSkipVerify: true in the account config to accept them.

Quick start (one command)

make test-integration

This starts a Greenmail container, runs all integration tests, then tears down the container — regardless of pass/fail.

Manual step-by-step

If you need to iterate on tests without restarting the container each time:

1. Start Greenmail

   docker run -d --name greenmail \
     -p 3465:3465 -p 3993:3993 \
     -e "GREENMAIL_OPTS=-Dgreenmail.setup.test.all -Dgreenmail.users=test:password@example.com -Dgreenmail.hostname=0.0.0.0" \
     greenmail/standalone:2.1.0
   

   Wait ~3 seconds for the JVM to start.

2. Run integration tests

   TEST_IMAP_HOST=localhost TEST_IMAP_PORT=3993 \
   TEST_SMTP_HOST=localhost TEST_SMTP_PORT=3465 \
   TEST_EMAIL=test@example.com TEST_PASSWORD=password \
     go test -tags=integration -race -v ./...
   

3. Tear down when done

   docker stop greenmail && docker rm greenmail
   

Test environment variables

Variable	Required	Default	Description
TEST_IMAP_HOST	Yes*	—	IMAP server hostname. Tests skip if unset.
TEST_IMAP_PORT	No	3993	IMAPS port
TEST_SMTP_HOST	Yes*	—	SMTP server hostname. Tests skip if unset.
TEST_SMTP_PORT	No	3465	SMTPS port
TEST_EMAIL	No	test@example.com	Email address for the test account
TEST_USERNAME	No	Local part of TEST_EMAIL	IMAP/SMTP login username (Greenmail uses local part only)
TEST_PASSWORD	No	password	Account password

*If the corresponding HOST variable is unset, that test file's tests are skipped with a message (not failed).

What the tests cover

IMAP (internal/imap/integration_test.go — 7 tests):

Test	What it verifies
ConnectAndListFolders	TLS connection, authentication, folder listing, INBOX exists
SendAndListMessages	SMTP send → IMAP receive round-trip, body content match
SearchBySubject	IMAP SEARCH by subject string
DeleteMessagePermanent	Flag as deleted + expunge, verify message is gone
MoveMessage	IMAP MOVE to another folder (skips if server lacks MOVE extension)
DraftWorkflow	SaveDraft → GetDraft → DeleteDraft lifecycle (skips if no APPENDUID)
MarkReadAndFlag	Set read/flagged flags, verify via GetMessage

SMTP (internal/smtp/integration_test.go — 4 tests):

Test	What it verifies
SendPlainText	Plain-text email delivery, body content verified via IMAP
SendHTML	HTML email delivery, Content-Type verified as text/html
SendWithAttachment	Multipart MIME with attachment, filename verified in metadata
RateLimitTokenConsumption	Sending consumes a rate-limit token

Troubleshooting

Symptom	Cause	Fix
EOF or connection reset on connect	Greenmail bound to 127.0.0.1 inside container	Add -Dgreenmail.hostname=0.0.0.0 to GREENMAIL_OPTS
TLS handshake failure / certificate error	Self-signed certs rejected	Test configs already set InsecureSkipVerify: true — if writing new tests, do the same
Invalid login/password	Using full email as username	Greenmail expects the local part only (test, not test@example.com). Set TEST_USERNAME or let it default.
STARTTLS error on port 3993	Using STARTTLS on an implicit-TLS port	Test configs set UseStartTLS=false. Don't use ports 3143/3025 (plain, no TLS).
Tests skip with "not set"	TEST_IMAP_HOST / TEST_SMTP_HOST not exported	Export the env vars or use the make test-integration target
MoveMessage test skips	Greenmail may not support MOVE	Expected — test uses t.Skip()

CI

Integration tests run automatically in GitHub Actions via the integration job in .github/workflows/ci.yml. The job uses a Greenmail service container — no manual Docker setup needed. See the workflow file for the exact configuration.

Coverage

To generate a combined unit + integration coverage report:

# With Greenmail running (see above):
TEST_IMAP_HOST=localhost TEST_IMAP_PORT=3993 \
TEST_SMTP_HOST=localhost TEST_SMTP_PORT=3465 \
TEST_EMAIL=test@example.com TEST_PASSWORD=password \
  go test -tags=integration -race -coverprofile=coverage.out ./...

go tool cover -func=coverage.out | tail -1   # total percentage
go tool cover -html=coverage.out             # open in browser

Architecture

mcp-server-email/
├── cmd/mcp-server-email/     # Entry point
└── internal/
    ├── auth/                 # OAuth2 device code flow, XOAUTH2 SASL, token store
    ├── config/               # Multi-account configuration, provider auto-detection
    ├── imap/                 # IMAP client (split by concern), connection pool, Operations interface
    │   ├── client.go         # Client struct, lifecycle, shared helpers
    │   ├── client_messages.go # List, search, get, attachments
    │   ├── client_folders.go  # Folder ops, role cache
    │   ├── client_drafts.go   # Draft save/get/delete
    │   ├── client_flags.go    # Flags, move, copy, delete
    │   └── pool.go           # Connection pool with configurable close timeout
    ├── log/                  # Structured logging (slog) initialization
    ├── models/               # Email model, message ID codec, error types
    ├── resources/            # email://status resource
    ├── retry/                # Token-bucket rate limiter
    ├── smtp/                 # SMTP client, Operations interface
    └── tools/                # 22 MCP tool handlers + registration

Tool handlers are decoupled from IMAP/SMTP clients via the imap.Operations and smtp.Operations interfaces, enabling comprehensive unit testing with mocks.

Dependencies

This project uses go-imap v2 (currently v2.0.0-beta.8). The v2 API is not yet stable — breaking changes may occur before the v2.0.0 release. We pin the exact version in go.mod and will upgrade promptly when stable is released.

License

MIT