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The logger plugin provides visibility into SMTP server activity by logging each SMTP phase to the console. This is useful for debugging, monitoring, and auditing email traffic.

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What It Does

The logger plugin hooks into key SMTP lifecycle events and outputs information about:
  • New client connections
  • MAIL FROM commands (sender addresses)
  • RCPT TO commands (recipient addresses)
  • Connection closures
Each log entry is prefixed with the event type and includes relevant connection or address information.

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Function Signature

function logger(): Plugin
The logger function takes no parameters and returns a Fumi plugin.

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Usage

Import and use the logger plugin in your Fumi application: 
import { Fumi } from "@puiusabin/fumi";
import { logger } from "@puiusabin/fumi/plugins/logger";

const app = new Fumi();

// Add the logger plugin
app.use(logger());

await app.listen(2525);

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Example Output

When a client connects and sends an email, you’ll see output like: 
[connect] 192.168.1.100
[mail from] [email protected]
[rcpt to] [email protected]
[close] 192.168.1.100

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Implementation

The logger plugin hooks into four lifecycle events: 
export function logger(): Plugin {
  return (app) => {
    app.onConnect(async (ctx, next) => {
      console.log(`[connect] ${ctx.session.remoteAddress}`);
      await next();
    });

    app.onMailFrom(async (ctx, next) => {
      console.log(`[mail from] ${ctx.address.address}`);
      await next();
    });

    app.onRcptTo(async (ctx, next) => {
      console.log(`[rcpt to] ${ctx.address.address}`);
      await next();
    });

    app.onClose(async (ctx) => {
      console.log(`[close] ${ctx.session.remoteAddress}`);
    });
  };
}
The logger plugin writes to stdout using console.log. In production environments, consider redirecting output to a file or using a more sophisticated logging solution.

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Use Cases

  • Development: Monitor SMTP traffic during local development
  • Debugging: Trace connection and command flow to diagnose issues
  • Auditing: Keep simple logs of email activity
  • Testing: Verify that your SMTP server is receiving expected commands

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