Simple SMTP Mailer

Send emails via SMTP using the msmtp command-line tool configured in ~/.msmtp/config for authentication and server settings.

Security Scan

The skill is internally consistent with its stated purpose (sending mail via msmtp); it requests no unrelated credentials or installs, but remember it will use whatever SMTP credentials are stored in ~/.msmtp/config and can send outbound email, which is a powerful capability you should only enable when you trust the agent.

Purpose & Capability

Name/description claim (send mail via msmtp) matches the manifests and SKILL.md. _meta.json declares msmtp as a required binary and the docs instruct installing msmtp via package managers — consistent and proportionate.

Instruction Scope

SKILL.md and CLAUDE.md instruct the agent to run msmtp commands and to use ~/.msmtp/config for credentials, which is expected. Note: CLAUDE.md contains hardcoded example path (/Users/yugaoxiang/.msmtp/config) that is inconsistent with the documented ~/.msmtp/config and appears to be a leftover from a developer environment — harmless but confusing. Troubleshooting advice includes 'tls_certcheck off', which reduces TLS security and should be avoided in production.

Install Mechanism

No custom install script; install hints use standard package managers (brew/apt/dnf) declared in _meta.json. These are low-risk, well-known install mechanisms.

Credentials

The skill requests no environment variables but depends on the user's ~/.msmtp/config, which stores SMTP username/password. That is appropriate for a mail sender, but it means the agent will have access to credentials stored there and can send arbitrary outbound mail. Users should ensure those credentials are scoped (use app-specific passwords) and understand the exfiltration risk inherent to sending email.

Persistence & Privilege

always is false and the skill is user-invocable. Model invocation is allowed (the platform default) but the skill is not forced into every session. There is no indication the skill attempts to modify other skills or system-wide settings.

Assessment

This skill appears to do what it says: run the msmtp CLI using your ~/.msmtp/config. Before installing, consider: 1) the agent will use whatever SMTP credentials are in that file — prefer app-specific passwords and minimal-permission accounts; 2) review and secure ~/.msmtp/config (chmod 600) and avoid placing highly privileged credentials there; 3) be aware the agent can send arbitrary outbound emails (a potential data-exfiltration channel); 4) the CLAUDE.md includes a hardcoded home path (/Users/yugaoxiang/.msmtp/config) — the real config is ~/.msmtp/config on your system; 5) avoid following the advice to disable TLS certificate checks in production. If you only need to send occasional messages, consider manually running msmtp or creating a narrowly scoped SMTP account for the skill rather than exposing your primary email credentials.

Simple SMTP Mail

Send emails via SMTP using msmtp command-line tool.

Configuration

Create a configuration file at ~/.msmtp/config with the following format:

account default
host <SMTP_SERVER>
port <PORT>
tls on
tls_starttls off
auth on
user <EMAIL_ADDRESS>
password <PASSWORD>
from <EMAIL_ADDRESS>

Common SMTP Settings

Gmail:

• SMTP Server: smtp.gmail.com
• Port: 465 (SSL) or 587 (TLS)
• Note: Use App Password, not your regular password

QQ Mail:

• SMTP Server: smtp.qq.com
• Port: 465

Outlook/Hotmail:

• SMTP Server: smtp.office365.com
• Port: 587

163.com:

• SMTP Server: smtp.163.com
• Port: 465

Installation

1. Install msmtp

macOS:

brew install msmtp

Linux (Debian/Ubuntu):

sudo apt install msmtp

Linux (Fedora/RHEL):

sudo dnf install msmtp

2. Configure SMTP

Edit ~/.msmtp/config:

nano ~/.msmtp/config

3. Set Permissions

chmod 600 ~/.msmtp/config

Sending Email

Basic Email

echo "Body text" | msmtp [e-mail]

With Subject

echo -e "Subject: Your Subject\n\nBody text" | msmtp [e-mail]

With Subject and From Header

echo -e "Subject: Your Subject\nFrom: [e-mail]\n\nBody text" | msmtp [e-mail]

HTML Content

echo -e "Subject: Your Subject\nContent-Type: text/html; charset=UTF-8\n\n<html>...</html>" | msmtp [e-mail]

Testing

Check if SMTP server is reachable:

msmtp --file=~/.msmtp/config --serverinfo

Troubleshooting

• "Account not found": Check your config file path with --file flag
• "Authentication failed": Verify username and password (or App Password)
• "Connection refused": Check port number and firewall settings
• "TLS certificate error": Try tls_certcheck off in config (not recommended for production)