SMTP MCP Server

io.github.ni-c/smtp-mcp

Repository Registry

What is the SMTP MCP server?

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

How to install SMTP

Copy-paste configuration for popular MCP clients.

transport: stdio

Config generated by PluginBench — verify against the source before use.

Environment / auth

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
required
secret
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_REPLY_TO
Reply-To header on every message, e.g. "Team <team@example.net>". Unset means no Reply-To header and replies go to SMTP_FROM. There is no reply_to 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.

~/Library/Application Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "smtp-mcp": {
      "command": "npx",
      "args": [
        "-y",
        "@ni-c/smtp-mcp"
      ],
      "env": {
        "SMTP_HOST": "<YOUR_SMTP_HOST>",
        "SMTP_PORT": "<YOUR_SMTP_PORT>",
        "SMTP_TLS": "<YOUR_SMTP_TLS>",
        "SMTP_USER": "<YOUR_SMTP_USER>",
        "SMTP_PASSWORD": "<YOUR_SMTP_PASSWORD>",
        "SMTP_FROM": "<YOUR_SMTP_FROM>",
        "SMTP_REPLY_TO": "<YOUR_SMTP_REPLY_TO>",
        "SMTP_ALLOW_SEND": "<YOUR_SMTP_ALLOW_SEND>",
        "SMTP_ALLOWED_RECIPIENTS": "<YOUR_SMTP_ALLOWED_RECIPIENTS>",
        "SMTP_MAX_RECIPIENTS": "<YOUR_SMTP_MAX_RECIPIENTS>",
        "SMTP_MAX_SENDS_PER_HOUR": "<YOUR_SMTP_MAX_SENDS_PER_HOUR>",
        "SMTP_MAX_MESSAGE_BYTES": "<YOUR_SMTP_MAX_MESSAGE_BYTES>",
        "SMTP_MAX_ATTACHMENT_BYTES": "<YOUR_SMTP_MAX_ATTACHMENT_BYTES>",
        "SMTP_ATTACHMENT_DIR": "<YOUR_SMTP_ATTACHMENT_DIR>",
        "SMTP_ATTACHMENT_TYPES": "<YOUR_SMTP_ATTACHMENT_TYPES>",
        "SMTP_SIGNATURE": "<YOUR_SMTP_SIGNATURE>",
        "SMTP_AUDIT_LOG": "<YOUR_SMTP_AUDIT_LOG>",
        "SMTP_ALLOW_TOOLS": "<YOUR_SMTP_ALLOW_TOOLS>",
        "SMTP_DENY_TOOLS": "<YOUR_SMTP_DENY_TOOLS>",
        "SMTP_INSECURE_TLS": "<YOUR_SMTP_INSECURE_TLS>"
      }
    }
  }
}

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