Mailchimp Email Campaign Sender

A small Go application that reads recipients from a CSV file, renders an HTML/text email template for each recipient, sends the messages through SMTP, and logs delivery results to a local SQLite database.

What it does

• Loads recipients from emails.csv
• Renders email.tmpl for each recipient using Go templates
• Sends email through an SMTP server
• Stores send/failure history in SQLite
• Prints a final campaign summary with totals and failed deliveries

Project layout

• main.go - application entry point and worker orchestration
• config.go - environment-driven configuration loading
• consumer.go - CSV reader that streams recipients into a channel
• producer.go - worker logic that renders templates and sends email
• database.go - SQLite initialization and logging helpers
• email.tmpl - email template used for each recipient
• emails.csv - sample recipient list
• info.md - extra notes for the project

How it works

1. The app reads runtime settings from environment variables.
2. A SQLite database is created if it does not already exist.
3. Recipients are loaded from the CSV file and sent to workers through a channel.
4. Each worker renders the template with recipient data.
5. The email is sent with net/smtp.
6. Successes and failures are written to the email_logs table.
7. When all workers finish, the app prints delivery statistics and any failed emails.

Requirements

• Go 1.25 or newer
• An SMTP server for local testing or real delivery
• SQLite is embedded through the Go dependency, so no separate database server is needed

Recommended local SMTP setup

For local testing, Mailpit is a convenient SMTP sink that accepts messages and exposes a web UI.

docker run -d --restart unless-stopped --name mailpit -p 8025:8025 -p 1025:1025 axllent/mailpit

If localhost resolves to IPv6 on your machine, use 127.0.0.1 for the SMTP host.

Mailpit UI: http://localhost:8025

Configuration

The app is configured entirely through environment variables. Every value has a default.

Variable	Default	Purpose
MAILCHIMP_DB_PATH	mailchimp.db	Path to the SQLite database file
MAILCHIMP_EMAILS_CSV	./emails.csv	Path to the recipient CSV file
MAILCHIMP_TEMPLATE_PATH	email.tmpl	Path to the email template file
MAILCHIMP_SMTP_HOST	127.0.0.1	SMTP server host
MAILCHIMP_SMTP_PORT	1025	SMTP server port
MAILCHIMP_SENDER_EMAIL	shreyashukla20042005@gmail.com	Sender address used in SMTP delivery
MAILCHIMP_WORKER_COUNT	5	Number of concurrent email workers
MAILCHIMP_SEND_DELAY_MS	50	Delay between sends per worker in milliseconds

Example configuration

PowerShell

$env:MAILCHIMP_SMTP_HOST = "127.0.0.1"
$env:MAILCHIMP_SMTP_PORT = "1025"
$env:MAILCHIMP_SENDER_EMAIL = "sender@example.com"
$env:MAILCHIMP_WORKER_COUNT = "5"
$env:MAILCHIMP_SEND_DELAY_MS = "50"

Bash

export MAILCHIMP_SMTP_HOST=127.0.0.1
export MAILCHIMP_SMTP_PORT=1025
export MAILCHIMP_SENDER_EMAIL=sender@example.com
export MAILCHIMP_WORKER_COUNT=5
export MAILCHIMP_SEND_DELAY_MS=50

Running the app

From the project root:

go run .

If you want to point at a different CSV, template, or database file, set the environment variables before running.

Input files

CSV format

The CSV file must include a header row with at least these columns:

• name
• email

Example:

name,email
Alice Johnson,alice.johnson@example.com
Bob Smith,bob.smith@example.com

Template format

The template is rendered with a Recipient object that exposes Name and Email.

Example:

Subject: Hello, {{.Name}}

Hi {{.Name}}

Thanks,
Shreya

Database schema

The application creates an email_logs table automatically.

Columns:

• email - recipient email address
• name - recipient name
• status - sent or failed
• failure_type - failure category such as template_error or smtp_error
• error_msg - error message from the send attempt
• attempts - retry count recorded by the app
• sent_at - timestamp for successful sends
• failed_at - timestamp for failed sends
• created_at - row creation timestamp

Output

At the end of a run, the app prints:

• Total rows logged
• Count of sent emails
• Count of failed emails
• A list of failed recipients when failures occurred

Troubleshooting

• If nothing is sent, confirm the SMTP host and port are reachable.
• If template parsing fails, check that email.tmpl exists and contains valid Go template syntax.
• If the CSV fails to load, make sure the first row is a header and the data rows have at least two columns.
• If the database file cannot be created, verify that the working directory is writable.
• If you are testing with Mailpit, open the UI at http://localhost:8025 to inspect received messages.

Notes

• The sender address is configurable, but the current default in code is a sample personal address. Override it for real use.
• Failed sends are logged immediately and included in the final summary.
• The worker count and per-send delay make it easy to tune throughput while testing.