MCP Email Server

An MCP (Model Context Protocol) server built with Quarkus that exposes common email operations as tools for LLM clients like Claude. Supports multiple named email accounts (e.g., work + Gmail) from a single server instance.

WARNING: This server performs real operations on your mailbox — moving, deleting, and sending emails. Always ensure you have a backup of your Maildir / emails before use. The author assumes no responsibility for any loss of data or unintended consequences resulting from the use of this MCP server. Use at your own risk.

Features / Tools

| Tool | Description | |------|-------------| | listAccounts | List configured account names (call first to discover accounts) | | listFolders | List all mail folders (INBOX, Sent, Drafts, etc.) | | listFolderTree | Full folder hierarchy with message/unread counts | | listEmails | List emails in a folder with pagination | | readEmail | Read the full content of a specific email | | getNextUnreadEmail | Get oldest unread email with all headers (for spam triage) | | triageUnread | Quick-scan unread emails — headers only, no body | | getUnreadCount | Count unread emails in a folder | | getSpamFolder | Auto-detect and cache the spam/junk folder | | setSpamFolder | Manually override the spam folder | | moveToSpam | Move an email to the cached spam folder | | moveEmail | Move an email between folders | | moveEmails | Batch move multiple emails in one operation | | deleteEmail | Delete an email (moves to Trash by default) | | searchEmails | Search by subject, sender, or body | | sendEmail | Send an email via SMTP | | replyEmail | Reply to an email with proper threading headers | | forwardEmail | Verbatim forward (body never enters LLM context) | | forwardEmailWithComment | Forward with a comment prepended | | markEmail | Mark an email as read/unread | | markEmails | Batch mark multiple emails as read/unread | | flagEmail | Flag/star emails (IMAP \Flagged) with optional follow-up date | | saveDraft | Save a draft email for user review | | createFolder | Create a new mail folder |

All tools (except listAccounts) require an account parameter — the name of the account to operate on (e.g., work, gmail).

Prerequisites

Java 21+ (tested with JDK 25)
Maven 3.9+ (only needed for building)

Build

# Build the uber-jar
mvn package -DskipTests

# The artifact will be at:
# target/mcp-email-server-1.0.0-SNAPSHOT-runner.jar

Note: Maven must use Java 21+. If your system Maven defaults to an older JDK, set JAVA_HOME before building:

mvn package -DskipTests

Configuration

All credentials are passed via environment variables — nothing sensitive goes in source control. The LLM never sees these variables — it only sees tool names/descriptions and the text your tools return.

Accounts are defined by convention: EMAIL_ACCOUNTS_<NAME>_IMAP_* and EMAIL_ACCOUNTS_<NAME>_SMTP_*, where <NAME> is the account name in uppercase.

Per-account variables

| Variable pattern | Required | Default | Example | |-----------------|----------|---------|---------| | EMAIL_ACCOUNTS_<NAME>_IMAP_HOST | yes | | imap.gmail.com | | EMAIL_ACCOUNTS_<NAME>_IMAP_USERNAME | yes | | you@gmail.com | | EMAIL_ACCOUNTS_<NAME>_IMAP_PASSWORD | yes | | abcd efgh ijkl mnop | | EMAIL_ACCOUNTS_<NAME>_IMAP_PORT | no | 993 | | | EMAIL_ACCOUNTS_<NAME>_IMAP_SSL | no | true | | | EMAIL_ACCOUNTS_<NAME>_SMTP_HOST | yes | | smtp.gmail.com | | EMAIL_ACCOUNTS_<NAME>_SMTP_USERNAME | yes | | you@gmail.com | | EMAIL_ACCOUNTS_<NAME>_SMTP_PASSWORD | yes | | abcd efgh ijkl mnop | | EMAIL_ACCOUNTS_<NAME>_SMTP_PORT | no | 587 | | | EMAIL_ACCOUNTS_<NAME>_SMTP_STARTTLS | no | true | |

For Gmail, create an App Password.

You can define as many accounts as needed. For example, to add a work and gmail account, set environment variables for both EMAIL_ACCOUNTS_WORK_* and EMAIL_ACCOUNTS_GMAIL_*.

Setting up with Claude Desktop

Build the uber-jar (see above).
Edit the Claude Desktop config file claude_desktop_config.json. On Windows it is located at C:\Users\<UserName>\AppData\Roaming\Claude\claude_desktop_config.json. On macOS it is at ~/Library/Application Support/Claude/claude_desktop_config.json.
Add the email entry to the mcpServers section. Here is an example with two accounts (work and gmail):

{
  "mcpServers": {
    "email": {
      "command": "java",
      "args": [
        "-Dquarkus.mcp.server.stdio.enabled=true",
        "-jar",
        "C:\\Users\\YourName\\path\\to\\mcp-email-server-1.0.0-SNAPSHOT-runner.jar"
      ],
      "env": {
        "EMAIL_ACCOUNTS_WORK_IMAP_HOST": "imap.example.com",
        "EMAIL_ACCOUNTS_WORK_IMAP_USERNAME": "user@example.com",
        "EMAIL_ACCOUNTS_WORK_IMAP_PASSWORD": "your-app-password",
        "EMAIL_ACCOUNTS_WORK_SMTP_HOST": "smtp.example.com",
        "EMAIL_ACCOUNTS_WORK_SMTP_USERNAME": "user@example.com",
        "EMAIL_ACCOUNTS_WORK_SMTP_PASSWORD": "your-app-password",
        "EMAIL_ACCOUNTS_GMAIL_IMAP_HOST": "imap.gmail.com",
        "EMAIL_ACCOUNTS_GMAIL_IMAP_USERNAME": "you@gmail.com",
        "EMAIL_ACCOUNTS_GMAIL_IMAP_PASSWORD": "your-gmail-app-password",
        "EMAIL_ACCOUNTS_GMAIL_SMTP_HOST": "smtp.gmail.com",
        "EMAIL_ACCOUNTS_GMAIL_SMTP_USERNAME": "you@gmail.com",
        "EMAIL_ACCOUNTS_GMAIL_SMTP_PASSWORD": "your-gmail-app-password"
      }
    }
  }
}

Restart Claude Desktop. The email tools should appear in the tool list.

Setting up with Claude Code

Add the same config to your Claude Code MCP settings (~/.claude/settings.json or project-level .claude/settings.json).

Troubleshooting

Server disconnects immediately: make sure -Dquarkus.mcp.server.stdio.enabled=true is in the args before -jar.
No log output visible: Quarkus logs go to mcp-email-server.log (in the working directory), not to stdout/stderr, to avoid interfering with the STDIO transport. Check that file for errors.
Authentication errors: for Gmail, you need an App Password, not your regular password. Make sure 2-Step Verification is enabled on your Google account first.
Build fails: ensure JAVA_HOME points to JDK 21+. The system java on PATH may differ from what Maven uses.
"Unknown account" errors: call listAccounts first to see which accounts are configured. Account names are lowercase as defined in the environment variables (e.g., work, gmail).

MCP Servers