mcp-email-server 0.16.0

IMAP and SMTP via MCP Server

mcp-email-server

IMAP and SMTP via MCP Server

• Github repository: https://github.com/ai-zerolab/mcp-email-server/
• Documentation https://ai-zerolab.github.io/mcp-email-server/

Installation

Manual Installation

We recommend using uv to manage your environment.

Try uvx mcp-email-server@latest ui to config, and use following configuration for mcp client:

{
  "mcpServers": {
    "zerolib-email": {
      "command": "uvx",
      "args": ["mcp-email-server@latest", "stdio"]
    }
  }
}

This package is available on PyPI, so you can install it using pip install mcp-email-server

After that, configure your email server using the ui: mcp-email-server ui

Credential Storage

Accounts added via the UI or the add_email_account tool are persisted to a TOML file at ~/.config/zerolib/mcp_email_server/config.toml. Where the actual passwords/API keys live depends on credential_storage (also settable via MCP_EMAIL_SERVER_CREDENTIAL_STORAGE), one of:

• auto (default): store credentials in the OS keyring — macOS Keychain, Linux Secret Service (GNOME Keyring / KWallet) — when a usable backend is detected; otherwise fall back to the plaintext TOML file (0o600 permissions, owner-only). Falls back automatically on headless Linux, Docker, or any environment without a D-Bus session.
• keyring: require the OS keyring; fail loudly instead of silently falling back if no backend is usable.
• plaintext: never touch the keyring. Useful for containers, CI, or if you simply prefer a portable config file.

When credentials are keyring-backed, the TOML file stores only a placeholder (__KEYRING__) and non-secret metadata — the real secret lives in the OS keyring under service mcp-email-server, one entry per <account_name>:<incoming|outgoing|api_key> (viewable in Keychain Access on macOS, or Seahorse on Linux).

Migrating an existing config between storage modes:

mcp-email-server migrate-credentials --to keyring    # move plaintext secrets into the OS keyring
mcp-email-server migrate-credentials --to plaintext  # move keyring secrets back into the TOML file

Migration also happens implicitly: any time you add/edit an account while credential_storage is auto or keyring with a usable backend, that account's secrets move into the keyring on the next save. If MCP_EMAIL_SERVER_CREDENTIAL_STORAGE is active during a save, its effective mode is persisted too, keeping the mode marker consistent with the credential representation written to the same file.

Failure modes & troubleshooting

• Server won't start / UI won't load accounts, keychain-related error: the OS keyring is locked or unreachable. This is expected if credentials are keyring-backed — the secret simply isn't in the config file. Unlock your keychain, or run mcp-email-server migrate-credentials --to plaintext if you'd rather not depend on it.
• credential_storage is 'plaintext' but the config references keyring-stored credentials: run migrate-credentials --to plaintext, or unset MCP_EMAIL_SERVER_CREDENTIAL_STORAGE / the credential_storage setting so the config can resolve them from the keyring instead.
• macOS Keychain access prompt, or the server can't read a secret it wrote earlier: Keychain ACLs are per-application. If the server is spawned via uvx (as in the Claude Desktop config above), a fresh uvx resolution can present a different binary path than the one that stored the secret, triggering a "Keychain wants to use a password" prompt. Choose "Always Allow" the first time this happens.
• A migration seems to have had no effect: if MCP_EMAIL_SERVER_CREDENTIAL_STORAGE is set in your environment, it takes precedence over whatever migrate-credentials --to ... just wrote to the file on every subsequent run. Unset it, or keep it in sync with your intended mode.

Known limitations

• Non-POSIX (Windows) file permissions: the 0o600 owner-only guarantee on the plaintext TOML is enforced only on POSIX systems. On Windows the file is written without an owner-restricted ACL, so prefer keyring mode (Windows Credential Locker) there when secrets must not be readable by other accounts.
• auto/keyring trusts whatever keyring backend is active: usability is decided by a live set/get round-trip, not by the backend's storage guarantees. A third-party keyring plugin that persists secrets in plaintext would pass that probe. If you install custom keyring backends, verify the active one (keyring --list-backends) stores secrets securely.
• Keyring and TOML writes are not transactional: a save pushes secrets to the keyring and then rewrites the TOML. The TOML rewrite is atomic on its own (temp file + os.replace), but a crash between the two steps can leave a keyring entry with no matching config reference (an orphaned secret), or a config reference whose keyring write partly failed. A plaintext migration reports keyring entries it could not remove so you can clean them up manually.

Environment Variable Configuration

You can also configure the email server using environment variables, which is particularly useful for CI/CD environments like Jenkins. zerolib-email supports both UI configuration (via TOML file) and environment variables, with environment variables taking precedence.

{
  "mcpServers": {
    "zerolib-email": {
      "command": "uvx",
      "args": ["mcp-email-server@latest", "stdio"],
      "env": {
        "MCP_EMAIL_SERVER_ACCOUNT_NAME": "work",
        "MCP_EMAIL_SERVER_FULL_NAME": "John Doe",
        "MCP_EMAIL_SERVER_EMAIL_ADDRESS": "[e-mail]",
        "MCP_EMAIL_SERVER_USER_NAME": "[e-mail]",
        "MCP_EMAIL_SERVER_PASSWORD": "your_password",
        "MCP_EMAIL_SERVER_IMAP_HOST": "imap.gmail.com",
        "MCP_EMAIL_SERVER_IMAP_PORT": "993",
        "MCP_EMAIL_SERVER_SMTP_HOST": "smtp.gmail.com",
        "MCP_EMAIL_SERVER_SMTP_PORT": "465"
      }
    }
  }
}

Available Environment Variables

Variable	Description	Default	Required
MCP_EMAIL_SERVER_ACCOUNT_NAME	Account identifier	"default"	No
MCP_EMAIL_SERVER_FULL_NAME	Display name	Email prefix	No
MCP_EMAIL_SERVER_EMAIL_ADDRESS	Email address	-	Yes
MCP_EMAIL_SERVER_USER_NAME	Login username	Same as email	No
MCP_EMAIL_SERVER_PASSWORD	Email password	-	Yes
MCP_EMAIL_SERVER_IMAP_HOST	IMAP server host	-	Yes
MCP_EMAIL_SERVER_IMAP_PORT	IMAP server port	993	No
MCP_EMAIL_SERVER_IMAP_SSL	Enable IMAP SSL	true	No
MCP_EMAIL_SERVER_IMAP_START_SSL	Enable IMAP STARTTLS	false	No
MCP_EMAIL_SERVER_IMAP_VERIFY_SSL	Verify IMAP SSL certificates (disable for self-signed)	true	No
MCP_EMAIL_SERVER_SMTP_HOST	SMTP server host; omit for IMAP-only mode (no sending)	-	No
MCP_EMAIL_SERVER_SMTP_PORT	SMTP server port	465	No
MCP_EMAIL_SERVER_SMTP_SSL	Enable SMTP SSL	true	No
MCP_EMAIL_SERVER_SMTP_START_SSL	Enable STARTTLS	false	No
MCP_EMAIL_SERVER_SMTP_VERIFY_SSL	Verify SSL certificates (disable for self-signed)	true	No
MCP_EMAIL_SERVER_ENABLE_ATTACHMENT_DOWNLOAD	Enable attachment download	false	No
MCP_EMAIL_SERVER_SAVE_TO_SENT	Save sent emails to IMAP Sent folder	true	No
MCP_EMAIL_SERVER_SENT_FOLDER_NAME	Custom Sent folder name (auto-detect if not set)	-	No
MCP_EMAIL_SERVER_ALLOWED_RECIPIENTS	Recipient allowlist (comma-separated); empty = all	-	No
MCP_EMAIL_SERVER_ALLOWED_SENDERS	Sender allowlist (comma-separated globs); empty = all	-	No
MCP_EMAIL_SERVER_REPORT_BLOCKED_MUTATIONS	Report blocked mutations as failures (default: silent no-op)	false	No
MCP_EMAIL_SERVER_CREDENTIAL_STORAGE	Credential storage mode: auto, keyring, or plaintext	auto	No

IMAP-only mode (no SMTP)

SMTP configuration is optional. When MCP_EMAIL_SERVER_SMTP_HOST is omitted, the account runs in IMAP-only mode: send_email is hidden (when every configured email account lacks SMTP) and no mail can leave the server. Note that IMAP-only is not strictly read-only — IMAP-backed write tools such as save_to_mailbox (which composes a message and stores it in a folder via IMAP APPEND), delete_emails, move_emails, and archive_emails remain available.

{
  "mcpServers": {
    "zerolib-email": {
      "command": "uvx",
      "args": ["mcp-email-server@latest", "stdio"],
      "env": {
        "MCP_EMAIL_SERVER_EMAIL_ADDRESS": "[e-mail]",
        "MCP_EMAIL_SERVER_PASSWORD": "your_password",
        "MCP_EMAIL_SERVER_IMAP_HOST": "imap.gmail.com"
      }
    }
  }
}

HTTP Transport Security

HTTP transports (sse and streamable-http) validate request Host and Origin headers to protect against DNS rebinding attacks. Localhost is allowed by default. For Docker networks or reverse proxies, configure the expected service names explicitly.

Variable	Description	Default
MCP_HOST	HTTP bind host for streamable-http	localhost
MCP_PORT	HTTP bind port for streamable-http	9557
MCP_ALLOWED_HOSTS	Comma-separated allowed Host values. Supports host:* ports	Localhost hosts
MCP_ALLOWED_ORIGINS	Comma-separated allowed Origin values. Supports host:* ports	Localhost origins
MCP_ENABLE_DNS_REBINDING_PROTECTION	Enable DNS rebinding protection	true

Docker Compose example:

services:
  mcp-email-server:
    image: ghcr.io/ai-zerolab/mcp-email-server:latest
    command: ["streamable-http"]
    environment:
      MCP_HOST: 0.0.0.0
      MCP_PORT: 9557
      MCP_ALLOWED_HOSTS: mcp-email-server:*,localhost:*,127.0.0.1:*
      MCP_ALLOWED_ORIGINS: http://mcp-email-server:*,http://localhost:*,http://127.0.0.1:*

Bare host entries such as MCP_ALLOWED_HOSTS=mcp-email-server also allow any port on that host. MCP_ENABLE_DNS_REBINDING_PROTECTION=false, MCP_ALLOWED_HOSTS=*, or MCP_ALLOWED_ORIGINS=* disables Host and Origin validation entirely. Use those options only in isolated local development environments.

IPv6 literals in allowlists should use bracketed notation, such as [::1]:* and http://[::1]:*.

Enabling Attachment Downloads

By default, downloading email attachments is disabled for security reasons. To enable this feature, you can either:

Option 1: Environment Variable

{
  "mcpServers": {
    "zerolib-email": {
      "command": "uvx",
      "args": ["mcp-email-server@latest", "stdio"],
      "env": {
        "MCP_EMAIL_SERVER_ENABLE_ATTACHMENT_DOWNLOAD": "true"
      }
    }
  }
}

Option 2: TOML Configuration

Add enable_attachment_download = true to your TOML configuration file (~/.config/zerolib/mcp_email_server/config.toml):

enable_attachment_download = true

[[emails]]
# ... your email configuration

Once enabled, you can use the download_attachment tool to save email attachments to a specified path.

Saving Sent Emails to IMAP Sent Folder

By default, sent emails are automatically saved to your IMAP Sent folder. This ensures that emails sent via the MCP server appear in your email client (Thunderbird, webmail, etc.).

The server auto-detects common Sent folder names: Sent, INBOX.Sent, Sent Items, Sent Mail, [Gmail]/Sent Mail.

To specify a custom Sent folder name (useful for providers with non-standard folder names):

Option 1: Environment Variable

{
  "mcpServers": {
    "zerolib-email": {
      "command": "uvx",
      "args": ["mcp-email-server@latest", "stdio"],
      "env": {
        "MCP_EMAIL_SERVER_SENT_FOLDER_NAME": "INBOX.Sent"
      }
    }
  }
}

Option 2: TOML Configuration

[[emails]]
account_name = "work"
save_to_sent = true
sent_folder_name = "INBOX.Sent"
# ... rest of your email configuration

To disable saving to Sent folder, set MCP_EMAIL_SERVER_SAVE_TO_SENT=false or save_to_sent = false in your TOML config.

Restricting Recipients (Allowlist)

By default the server can send to any address. Set allowed_recipients to restrict both send_email and save_to_mailbox to a trusted set. Leave it empty (the default) to allow all.

allowed_recipients = ["[e-mail]", "[e-mail]"]

Or via environment variable (comma-separated):

MCP_EMAIL_SERVER_ALLOWED_RECIPIENTS="[e-mail],[e-mail]"

When configured, any To/CC/BCC address not on the list is rejected with a clear error. Matching is case-insensitive and understands the Name <[e-mail]> form. The list_allowed_recipients tool appears only when an allowlist is configured, so default installs keep a minimal tool surface.

Filtering Incoming Mail (Sender Allowlist)

By default all senders are visible. Set allowed_senders to show mail only from trusted senders. Patterns support globs (e.g. *@company.com) and exact addresses, matched case-insensitively. Leave it empty (the default) to show everything.

allowed_senders = ["*@company.com", "[e-mail]"]

Or via environment variable (comma-separated):

MCP_EMAIL_SERVER_ALLOWED_SENDERS="*@company.com,[e-mail]"

When configured, filtering is applied to inbound read and mutation paths: list_emails_metadata excludes non-allowed senders before pagination, so total and page sizes reflect only allowed mail; get_emails_content and download_attachment check the sender before reading a message, so a non-allowed message's body and attachments are never fetched or marked read, and it is reported as inaccessible — indistinguishable from a missing message. Mutation tools first check the sender and never delete, flag, or move blocked mail. The list_allowed_senders tool appears only when an allowlist is configured.

Scope: the allowlist protects every inbound path — read (list_emails_metadata, get_emails_content, download_attachment) and mutation (delete_emails, mark_emails_as_read, move_emails, archive_emails). A blocked sender's mail is never read, deleted, flagged, or moved.

Blocked mutations (report_blocked_mutations, default false): when a mutation targets a blocked sender's message, it is never performed. By default the result is reported as a successful no-op — indistinguishable from acting on a non-existent message, so the allowlist does not reveal that a hidden message exists. Set report_blocked_mutations = true (or MCP_EMAIL_SERVER_REPORT_BLOCKED_MUTATIONS=true) to instead report blocked UIDs as failures (explicit, but reveals a blocked-but-real message differs from a missing one).

Note: matching is against the message's From header — local filtering only, not sender authentication. A spoofed From will pass the allowlist, so this is not a substitute for provider-side SPF / DKIM / DMARC enforcement.

Self-Signed Certificates and IMAP STARTTLS (e.g., ProtonMail Bridge)

Local mail bridges such as ProtonMail Bridge commonly use STARTTLS with self-signed certificates. Configure IMAP with plaintext connect plus STARTTLS upgrade, and disable certificate verification for the local bridge certificate:

{
  "mcpServers": {
    "zerolib-email": {
      "command": "uvx",
      "args": ["mcp-email-server@latest", "stdio"],
      "env": {
        "MCP_EMAIL_SERVER_IMAP_HOST": "127.0.0.1",
        "MCP_EMAIL_SERVER_IMAP_PORT": "1143",
        "MCP_EMAIL_SERVER_IMAP_SSL": "false",
        "MCP_EMAIL_SERVER_IMAP_START_SSL": "true",
        "MCP_EMAIL_SERVER_IMAP_VERIFY_SSL": "false",
        "MCP_EMAIL_SERVER_SMTP_VERIFY_SSL": "false"
      }
    }
  }
}

Or in TOML configuration:

[[emails]]
account_name = "protonmail"
# ... other settings ...

[emails.incoming]
host = "127.0.0.1"
port = 1143
use_ssl = false
start_ssl = true
verify_ssl = false

[emails.outgoing]
verify_ssl = false

For separate IMAP/SMTP credentials, you can also use:

• MCP_EMAIL_SERVER_IMAP_USER_NAME / MCP_EMAIL_SERVER_IMAP_PASSWORD
• MCP_EMAIL_SERVER_SMTP_USER_NAME / MCP_EMAIL_SERVER_SMTP_PASSWORD

Then you can try it in Claude Desktop. If you want to intergrate it with other mcp client, run $which mcp-email-server for the path and configure it in your client like:

{
  "mcpServers": {
    "zerolib-email": {
      "command": "{{ ENTRYPOINT }}",
      "args": ["stdio"]
    }
  }
}

If docker is avaliable, you can try use docker image, but you may need to config it in your client using tools via MCP. The default config path is ~/.config/zerolib/mcp_email_server/config.toml

{
  "mcpServers": {
    "zerolib-email": {
      "command": "docker",
      "args": ["run", "-it", "ghcr.io/ai-zerolab/mcp-email-server:latest"]
    }
  }
}

Installing via Smithery

To install Email Server for Claude Desktop automatically via Smithery:

npx -y @smithery/cli install @ai-zerolab/mcp-email-server --client claude

Usage

Replying to Emails

To reply to an email with proper threading (so it appears in the same conversation in email clients):

1. First, fetch the original email to get its message_id:

emails = await get_emails_content(account_name="work", email_ids=["123"])
original = emails.emails[0]

2. Send your reply using in_reply_to and references:

await send_email(
    account_name="work",
    recipients=[original.sender],
    subject=f"Re: {original.subject}",
    body="Thank you for your email...",
    in_reply_to=original.message_id,
    references=original.message_id,
)

The in_reply_to parameter sets the In-Reply-To header, and references sets the References header. Both are used by email clients to thread conversations properly.

Development

This project is managed using uv.

Try make install to install the virtual environment and install the pre-commit hooks.

Use uv run mcp-email-server for local development.

Releasing a new version

• Create an API Token on PyPI.
• Add the API Token to your projects secrets with the name PYPI_TOKEN by visiting this page.
• Create a new release on Github.
• Create a new tag in the form *.*.*.

For more details, see here.