Zero‑Exposure SMTP Mail Sender (MGC Secure Edition)

Send emails securely without exposing SMTP passwords. Users store SMTP credentials and email scripts in MGC; AI executes scripts via mgc_run blackbox. AI never sees credentials, script content, or email body (when stored in MGC). Adapted to MGC 1.4.10.

Overview

Zero-Exposure SMTP Mail Sender is a documentation skill that teaches how to send emails securely without exposing SMTP credentials.

This skill uses MGC Blackbox 1.4.10 to achieve true zero-exposure:

• Users store SMTP credentials via MGC WebUI
• Users store email scripts in MGC (AI can assist writing)
• (Optional) Users can store email content separately for privacy
• AI executes scripts via mgc_run (1.4.7+ blackbox)
• AI never sees credentials, script content, or email body

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What This Skill Enables

After reading this documentation, you will understand how to:

• Store SMTP credentials securely via MGC WebUI
• Store email scripts in MGC (using argparse + parse_known_args)
• Execute scripts via mgc_run (1.4.7+ blackbox); AI sees only {pid, status} + result file path
• Build secure email workflows
• Optional: store email content separately so AI never sees subject/body

This skill does not provide executable code, only documentation.

---

Prerequisites

1. Install MGC Blackbox ≥ 1.4.10:

   bash

   pip install mgc-blackbox>=1.4.10
   

2. Start MGC: mgc (API at http://127.0.0.1:57219, WebUI at 57218)
3. MCP tools available: mgc_save, mgc_run, mgc_list, mgc_find, mgc_open_webui
4. Token file: ~/.mgc/database/mgc_black_box/.mgc_token

Sandbox mode (1.4.9+): When running inside a sandbox Agent (Trae Work / Workbuddy), install MGC in the system environment; otherwise MCP operations may be limited — in that case, call FastAPI directly at /api/mgc/sensitive/run.

---

Security Model

Traditional Approach (Unsafe)

text

AI → receives credentials → sends email
     ↓
  Credentials exposed to AI

This Skill Approach (Zero-Exposure)

text

User → stores credentials (WebUI) → stores email script (mgc_save)
                                                  ↓
AI → executes script (mgc_run) → script reads credentials locally
                                                  ↓
                                    AI only sees {pid, status} + result file

AI never sees credentials, script content, or email body.

---

Step 1: Store Credentials (User via WebUI)

Important: Credentials must be stored by the user manually via MGC WebUI (or AI via mgc_save on explicit user instruction).

1. Start MGC: mgc
2. Open WebUI: http://127.0.0.1:57218
3. Navigate to Save page
4. Fill in:

text

info_type:   "config"
info_owner:  "smtp_gmail"      # You choose this name
content:
{
  "address": "[e-mail]",
  "password": "app_specific_password",
  "smtp_server": "smtp.gmail.com",
  "smtp_port": 587
}

Remember: Tell AI the credential name (info_type=config, info_owner=smtp_gmail) but NEVER share the actual content.

Rotating credentials: mgc_save again with the same info_type/info_owner AND update_if_exists=true. Scripts will pick up the new credentials automatically.

---

Step 2: Store Email Script (User via mgc_save)

Create an email script with argparse (literal defaults only) and store it in MGC:

python

import smtplib
import os
import json
import argparse
import requests
import datetime
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart

# ========== Configuration ==========
# Replace these with your credential names (info_owner)
SMTP_CREDENTIAL_NAME = "smtp_gmail"           # SMTP credentials
EMAIL_CONTENT_NAME = "email_template_001"     # (Optional) Email content stored in MGC


def get_credential(cred_name):
    """Read credential from MGC local API. Script-internal only; AI never calls this."""
    token_path = os.path.expanduser("~/.mgc/database/mgc_black_box/.mgc_token")
    if not os.path.exists(token_path):
        return None
    with open(token_path) as f:
        token = f.read().strip()

    resp = requests.post(
        "http://127.0.0.1:57219/api/mgc/sensitive/get",
        headers={"X-MGC-Token": token, "Content-Type": "application/json"},
        json={"info_type": "config", "info_owner": cred_name, "action": "run"},
        timeout=10,
    )
    if resp.status_code == 200:
        data = resp.json()
        data_field = data.get("data")
        if isinstance(data_field, str):
            return json.loads(data_field)
        elif isinstance(data_field, dict):
            content = data_field.get("content", "")
            if content:
                return json.loads(content)
    return None


def get_email_content(content_name):
    """Read email content from MGC (optional privacy feature)."""
    token_path = os.path.expanduser("~/.mgc/database/mgc_black_box/.mgc_token")
    if not os.path.exists(token_path):
        return None
    with open(token_path) as f:
        token = f.read().strip()

    resp = requests.post(
        "http://127.0.0.1:57219/api/mgc/sensitive/get",
        headers={"X-MGC-Token": token, "Content-Type": "application/json"},
        json={"info_type": "config", "info_owner": content_name, "action": "run"},
        timeout=10,
    )
    if resp.status_code == 200:
        data = resp.json()
        data_field = data.get("data")
        if isinstance(data_field, str):
            return data_field
        elif isinstance(data_field, dict):
            return data_field.get("content", "")
    return None


def send_email(to_address, subject, body, use_stored_content=False):
    """Send email via SMTP."""
    cred = get_credential(SMTP_CREDENTIAL_NAME)
    if not cred:
        return {"success": False, "error": "Failed to get SMTP credentials"}

    if use_stored_content:
        stored_content = get_email_content(EMAIL_CONTENT_NAME)
        if stored_content:
            try:
                content_data = json.loads(stored_content)
                subject = content_data.get("subject", subject)
                body = content_data.get("body", body)
            except Exception:
                body = stored_content

    try:
        msg = MIMEMultipart()
        msg['From'] = cred['address']
        msg['To'] = to_address
        msg['Subject'] = subject
        msg.attach(MIMEText(body, 'plain', 'utf-8'))

        with smtplib.SMTP(cred["smtp_server"], cred["smtp_port"]) as server:
            server.starttls()
            server.login(cred["address"], cred["password"])
            server.sendmail(cred["address"], [to_address], msg.as_string())
        return {"success": True, "message": "Email sent successfully"}
    except Exception as e:
        return {"success": False, "error": str(e)}


def main():
    # ✅ Literal defaults only — MGC 1.4.10 auto-parses into ext02
    parser = argparse.ArgumentParser()
    parser.add_argument("--to", default="")
    parser.add_argument("--subject", default="")
    parser.add_argument("--body", default="")
    parser.add_argument("--use_stored_content", action="store_true")
    args, _ = parser.parse_known_args()  # ✅ parse_known_args avoids exit on unknown params

    result = send_email(
        to_address=args.to,
        subject=args.subject,
        body=args.body,
        use_stored_content=args.use_stored_content,
    )

    # Write result to file so AI can read it (mgc_run returns pid+status)
    out_dir = os.path.expanduser("~/mgc_outputs")
    os.makedirs(out_dir, exist_ok=True)
    out_path = os.path.join(
        out_dir, f"email_{datetime.datetime.now().strftime('%Y%m%d_%H%M%S')}.txt"
    )
    with open(out_path, "w", encoding="utf-8") as f:
        json.dump(result, f, ensure_ascii=False, indent=2)
    print(f"RESULT_FILE:{out_path}")


if __name__ == "__main__":
    main()

Store the script:

python

mgc_save(
    info_type="script",
    info_owner="send_email_script",
    ext01="python",
    content="<paste your script here>",
    update_if_exists=True
)
# MGC 1.4.10 auto-fills ext02 = '["--to", "", "--subject", "", "--body", ""]'
# (literal argparse defaults become a JSON array string)

---

Step 3: AI Executes Script (Zero-Exposure)

When user wants to send an email, AI only needs to know:

• Script name: send_email_script
• Credential name: smtp_gmail (provided by user)

AI invokes mgc_run (1.4.7+ blackbox):

python

import json

# Build ext02 as JSON array string (1.4.10 contract)
ext02 = json.dumps([
    "--to", "[e-mail]",
    "--subject", "Hello",
    "--body", "Message content",
])

result = mgc_run(
    info_type="script",
    info_owner="send_email_script",
    diff_1="send_email_script",   # schema 必填的区分字段；多条同 owner 时消歧，单条时任意非空字符串均可
    ext02=ext02                   # JSON array string, NOT dict
)
# Returns: {"pid": 12345, "status": "started"}
# AI reads the RESULT_FILE path from the script's stdout (via mgc output convention)

AI never sees:

• SMTP credentials
• Script content
• Email implementation details
• Email body (when stored as MGC content)

Optional: Privacy Mode (Email Body Stored in MGC)

For maximum privacy, store email body in MGC so AI never even sees it:

text

Tool: mgc_save
Parameters:
  info_type:   "config"
  info_owner:  "email_template_001"
  content:     "{\"subject\": \"Project Update\", \"body\": \"Confidential quarterly report...\"}"

Then AI invokes with --use_stored_content:

python

ext02 = json.dumps([
    "--to", "[e-mail]",
    "--use_stored_content",
])
result = mgc_run(
    info_type="script",
    info_owner="send_email_script",
    diff_1="send_email_script",
    ext02=ext02
)
# Script reads body from MGC; AI only knows there's "some email" being sent to recipient

---

Security Boundaries

This Skill Provides

• Secure credential storage via MGC WebUI
• Script-based blackbox execution via mgc_run
• Privacy mode: email body can stay encrypted in MGC

This Skill Does NOT Provide

• Automated email sending
• Credential generation
• Script modification by AI (only assists writing)

⚠️ Important Warnings

1. Credentials must be stored via WebUI: AI should not handle credentials
2. Tell AI only credential name: info_type/info_owner, never the content
3. User must approve each send: AI cannot auto-send without authorization
4. Script content stays local: AI only executes, never reads
5. Use mgc_run, not mgc_get: mgc_get is deprecated for AI-driven script execution

---

MCP Tools Reference

mgc_save

Store email script:

python

mgc_save(
    info_type="script",
    info_owner="send_email_script",
    ext01="python",
    content="<script body>",
    update_if_exists=True   # required to overwrite same info_owner
)

Store SMTP credentials:

python

mgc_save(
    info_type="config",
    info_owner="smtp_gmail",
    content='{"address": "...", "password": "...", "smtp_server": "...", "smtp_port": 587}',
    update_if_exists=True
)

mgc_run (1.4.7+, recommended)

Execute email script — ext02 MUST be a JSON array string:

python

import json
result = mgc_run(
    info_type="script",
    info_owner="send_email_script",
    diff_1="send_email_script",
    ext02=json.dumps([
        "--to", "[e-mail]",
        "--subject", "Test",
        "--body", "Hello",
    ])
)
# Returns: {"pid": 12345, "status": "started"}

mgc_list

List stored entries (metadata only).

mgc_find (1.4.10 new)

python

# Fuzzy search for SMTP-related scripts/credentials
scripts = mgc_find(info_owner="smtp", match_mode="substring", limit=10)
# match_mode: substring / prefix / suffix / exact

mgc_open_webui

Opens WebUI for user to manage credentials and scripts.

---

Troubleshooting

Issue	Solution
mgc_run returns HTTP 422	ext02 MUST be a JSON array string like '["--to","[e-mail]"]'; use json.dumps(list)
dynamic_args_detected warning	Script uses dynamic argparse defaults (datetime.now() etc.). Switch to literal defaults or pass ext02 manually
args_not_recognized error	Source script's argparse did not recognize the args. Check add_argument names and ext02 array
Script execution fails	Check if credentials stored correctly in WebUI
Credential not found	Verify info_owner matches exactly (case-sensitive)
SMTP error	Check SMTP server/port settings; for Gmail use app-specific password
MGC not running	Run mgc in a terminal
Update not allowed	Add update_if_exists=true to mgc_save
Sandbox MCP unavailable	Install MGC in system environment, or call FastAPI at /api/mgc/sensitive/run

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Related Links

• Main Repository: https://github.com/zkeviny/MGC-Blackbox
• Issues: https://github.com/zkeviny/MGC-Blackbox/issues
• MGC Skills (WebUI → 1.4.7+): in-app button
• Contact: [e-mail]