SMTP

io.github.ni-c/smtp-mcpv0.1.0Email

MCP server that sends mail over SMTP, gated behind an allowlist and a human confirmation

The current version, v0.1.0, was published to the official MCP registry on 2026-09-03. It is distributed as @ni-c/smtp-mcp on npm and as the Docker image ghcr.io/ni-c/smtp-mcp:0.1.0, filed under Email by this index, and declares 19 environment variables. Removals and unreachable sources are measured across every server this index tracks, contract drift across the servers that answer in consecutive snapshots; the index's current counts put this record in context.

In-path gate · all MCP tools

Using SMTP in Claude, Cursor, Gemini CLI, Cline, or Zed?

MCP tool contracts can change remotely with no version bump. The mcpindex gate pins each contract and HOLDs the call when it drifts-before your agent acts. Zero credentials. This is not the package install for this server itself (use Install this server for that).

Install the mcpindex gate (one command)

Rewrites your MCP host config so each server launches behind the gate. Inspect first: curl -fsSL https://mcpindex.ai/install.sh | less

uv tool install mcpindex-gate && mcpindex-config-wire

Auditable install path →Watch it hold a drift →

Trust verdict · v1 advisory · method

NOT YET SCREENEDno verdict on file

Verdict not yet evaluated for this tool. The semantic screen takes adversarial cases first; coverage rolls out as the corpus expands (15/150 labels to graduation). The deterministic conformance probe is built but has not yet run on the public corpus, so a recorded verdict here is REVIEW or UNVERIFIED, never a clearing ALLOW. Until a verdict is recorded, an agent should treat this tool as not-yet-cleared and fall back to its own checks. Method: the eval, four-state verdict, honest limits.

Own this server? Screen its description →

That verdict was true at screening time (snapshot 2026-09-04).

Contracts can change after screening, with no version bump. The gate pins SMTP’s tool contracts on first sight and holds any silent change before your agent acts - the check that keeps being true on Tuesday.

See your first HOLD in 2 minutes →

Environment variables

SMTP_HOST

required

Hostname of the SMTP server, e.g. smtp.example.net.

SMTP_PORT

Port. Defaults to 587 for starttls, 465 for implicit, 25 for none.

SMTP_TLS

starttls (default), implicit or none. STARTTLS is required, never opportunistic.

SMTP_USER

required

Username for SMTP authentication.

SMTP_PASSWORD

requiredsecret

Password or app-specific password for SMTP authentication.

SMTP_FROM

required

The only sender this server will use, e.g. "Name <person@example.net>". There is no from parameter.

SMTP_ALLOW_SEND

Set to "true" to register the sending tools. Defaults to false: the server cannot send until it is set.

SMTP_ALLOWED_RECIPIENTS

Comma-separated addresses and @domains this server may write to. Required with SMTP_ALLOW_SEND=true; "*" allows any.

SMTP_MAX_RECIPIENTS

Maximum distinct recipients across To, Cc and Bcc in one message. Default 10.

SMTP_MAX_SENDS_PER_HOUR

Sliding hourly cap on messages sent. Default 20.

SMTP_MAX_MESSAGE_BYTES

Maximum size of the composed message. Default 10485760.

SMTP_MAX_ATTACHMENT_BYTES

Maximum size of a single attachment. Default 5242880.

SMTP_ATTACHMENT_DIR

Directory attachments are read from. Unset means attachments are unavailable.

SMTP_ATTACHMENT_TYPES

Comma-separated content types that may be attached. Defaults to a document and image allowlist.

SMTP_SIGNATURE

Text appended below the standard signature delimiter of every message.

SMTP_AUDIT_LOG

File the audit lines are appended to, in addition to stderr.

SMTP_ALLOW_TOOLS

Comma-separated tool names, a prefix with one trailing *, or "essential" for the curated preset.

SMTP_DENY_TOOLS

Comma-separated tool names or prefixes to remove, applied after SMTP_ALLOW_TOOLS.

SMTP_INSECURE_TLS

Set to "true" to accept self-signed certificates. Prefer a proper internal CA.

SMTP_HOST

required

Hostname of the SMTP server, e.g. smtp.example.net.

SMTP_PORT

Port. Defaults to 587 for starttls, 465 for implicit, 25 for none.

SMTP_TLS

starttls (default), implicit or none. STARTTLS is required, never opportunistic.

SMTP_USER

required

Username for SMTP authentication.

SMTP_PASSWORD

requiredsecret

Password or app-specific password for SMTP authentication.

SMTP_FROM

required

The only sender this server will use, e.g. "Name <person@example.net>". There is no from parameter.

SMTP_ALLOW_SEND

Set to "true" to register the sending tools. Defaults to false: the server cannot send until it is set.

SMTP_ALLOWED_RECIPIENTS

Comma-separated addresses and @domains this server may write to. Required with SMTP_ALLOW_SEND=true; "*" allows any.

SMTP_MAX_RECIPIENTS

Maximum distinct recipients across To, Cc and Bcc in one message. Default 10.

SMTP_MAX_SENDS_PER_HOUR

Sliding hourly cap on messages sent. Default 20.

SMTP_MAX_MESSAGE_BYTES

Maximum size of the composed message. Default 10485760.

SMTP_MAX_ATTACHMENT_BYTES

Maximum size of a single attachment. Default 5242880.

SMTP_ATTACHMENT_DIR

Directory attachments are read from. Unset means attachments are unavailable.

SMTP_ATTACHMENT_TYPES

Comma-separated content types that may be attached. Defaults to a document and image allowlist.

SMTP_SIGNATURE

Text appended below the standard signature delimiter of every message.

SMTP_AUDIT_LOG

File the audit lines are appended to, in addition to stderr.

SMTP_ALLOW_TOOLS

Comma-separated tool names, a prefix with one trailing *, or "essential" for the curated preset.

SMTP_DENY_TOOLS

Comma-separated tool names or prefixes to remove, applied after SMTP_ALLOW_TOOLS.

SMTP_INSECURE_TLS

Set to "true" to accept self-signed certificates. Prefer a proper internal CA.

MCP quality score · maturity, not trust · methodology

freshness

completeness

installability

documentation

stability

Alternatives in Email

Mermail

app.mermail/mcp

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MCP Emails

com.mcpemails/emails

Read, search, send, organize, draft and schedule email across your inboxes from any MCP client.

io.github.nikolausm/imap-mcp-server

IMAP/SMTP MCP server to search, read, organize, send, reply & forward email for AI assistants

Install this server

Claude Desktop (claude_desktop_config.json)

{
  "mcpServers": {
    "smtp-mcp": {
      "command": "npx",
      "args": [
        "-y",
        "--",
        "@ni-c/smtp-mcp"
      ],
      "env": {
        "SMTP_HOST": "<smtp_host>",
        "SMTP_PORT": "<smtp_port>",
        "SMTP_TLS": "<smtp_tls>",
        "SMTP_USER": "<smtp_user>",
        "SMTP_PASSWORD": "<your-smtp_password>",
        "SMTP_FROM": "<smtp_from>",
        "SMTP_ALLOW_SEND": "<smtp_allow_send>",
        "SMTP_ALLOWED_RECIPIENTS": "<smtp_allowed_recipients>",
        "SMTP_MAX_RECIPIENTS": "<smtp_max_recipients>",
        "SMTP_MAX_SENDS_PER_HOUR": "<smtp_max_sends_per_hour>",
        "SMTP_MAX_MESSAGE_BYTES": "<smtp_max_message_bytes>",
        "SMTP_MAX_ATTACHMENT_BYTES": "<smtp_max_attachment_bytes>",
        "SMTP_ATTACHMENT_DIR": "<smtp_attachment_dir>",
        "SMTP_ATTACHMENT_TYPES": "<smtp_attachment_types>",
        "SMTP_SIGNATURE": "<smtp_signature>",
        "SMTP_AUDIT_LOG": "<smtp_audit_log>",
        "SMTP_ALLOW_TOOLS": "<smtp_allow_tools>",
        "SMTP_DENY_TOOLS": "<smtp_deny_tools>",
        "SMTP_INSECURE_TLS": "<smtp_insecure_tls>"
      }
    }
  }
}

Cursor (.cursor/mcp.json)

{
  "mcpServers": {
    "smtp-mcp": {
      "command": "npx",
      "args": [
        "-y",
        "--",
        "@ni-c/smtp-mcp"
      ],
      "env": {
        "SMTP_HOST": "<smtp_host>",
        "SMTP_PORT": "<smtp_port>",
        "SMTP_TLS": "<smtp_tls>",
        "SMTP_USER": "<smtp_user>",
        "SMTP_PASSWORD": "<your-smtp_password>",
        "SMTP_FROM": "<smtp_from>",
        "SMTP_ALLOW_SEND": "<smtp_allow_send>",
        "SMTP_ALLOWED_RECIPIENTS": "<smtp_allowed_recipients>",
        "SMTP_MAX_RECIPIENTS": "<smtp_max_recipients>",
        "SMTP_MAX_SENDS_PER_HOUR": "<smtp_max_sends_per_hour>",
        "SMTP_MAX_MESSAGE_BYTES": "<smtp_max_message_bytes>",
        "SMTP_MAX_ATTACHMENT_BYTES": "<smtp_max_attachment_bytes>",
        "SMTP_ATTACHMENT_DIR": "<smtp_attachment_dir>",
        "SMTP_ATTACHMENT_TYPES": "<smtp_attachment_types>",
        "SMTP_SIGNATURE": "<smtp_signature>",
        "SMTP_AUDIT_LOG": "<smtp_audit_log>",
        "SMTP_ALLOW_TOOLS": "<smtp_allow_tools>",
        "SMTP_DENY_TOOLS": "<smtp_deny_tools>",
        "SMTP_INSECURE_TLS": "<smtp_insecure_tls>"
      }
    }
  }
}

Cline (cline_mcp_settings.json)

npx -y -- @ni-c/smtp-mcp

Claude Code (claude mcp add)

claude mcp add --scope user smtp-mcp -- npx -y -- @ni-c/smtp-mcp

Gemini CLI (gemini mcp add)

gemini mcp add -s user smtp-mcp npx -y -- @ni-c/smtp-mcp

Claude Desktop (Docker)

{
  "mcpServers": {
    "smtp-mcp": {
      "command": "docker",
      "args": [
        "run",
        "--rm",
        "-i",
        "--",
        "ghcr.io/ni-c/smtp-mcp:0.1.0"
      ],
      "env": {
        "SMTP_HOST": "<smtp_host>",
        "SMTP_PORT": "<smtp_port>",
        "SMTP_TLS": "<smtp_tls>",
        "SMTP_USER": "<smtp_user>",
        "SMTP_PASSWORD": "<your-smtp_password>",
        "SMTP_FROM": "<smtp_from>",
        "SMTP_ALLOW_SEND": "<smtp_allow_send>",
        "SMTP_ALLOWED_RECIPIENTS": "<smtp_allowed_recipients>",
        "SMTP_MAX_RECIPIENTS": "<smtp_max_recipients>",
        "SMTP_MAX_SENDS_PER_HOUR": "<smtp_max_sends_per_hour>",
        "SMTP_MAX_MESSAGE_BYTES": "<smtp_max_message_bytes>",
        "SMTP_MAX_ATTACHMENT_BYTES": "<smtp_max_attachment_bytes>",
        "SMTP_ATTACHMENT_DIR": "<smtp_attachment_dir>",
        "SMTP_ATTACHMENT_TYPES": "<smtp_attachment_types>",
        "SMTP_SIGNATURE": "<smtp_signature>",
        "SMTP_AUDIT_LOG": "<smtp_audit_log>",
        "SMTP_ALLOW_TOOLS": "<smtp_allow_tools>",
        "SMTP_DENY_TOOLS": "<smtp_deny_tools>",
        "SMTP_INSECURE_TLS": "<smtp_insecure_tls>"
      }
    }
  }
}

Verdict API

curl -s mcpindex.ai/api/v1/trust/server/io-github-ni-c-smtp-mcp

Free-tier verdict as JSON: decision + dimensions + severity. Call it from your agent before it invokes a tool it just discovered.

Details

version: v0.1.0
category: Email
quality: 90 / 100
operator: ni-c

Listing

Listed from the official MCP registry. Unclaimed by its maintainer. Maintainer? Email us →

Provenance

Each verdict is bound to a hash of the exact description it judged, so a re-crawl that changes the text produces a new record rather than silently inheriting this one. Verdict history is hash-chained and anchored to Bitcoin via OpenTimestamps (latest confirmed at block 965,260). Verify it yourself.

Links

Repository →Website →