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Tutorial Lengkap Membuat SMTP Relay Server dengan Mailcow + Docker

August 14, 2025 Tutorial by Masdika.ID

Panduan ini membahas langkah demi langkah membuat SMTP relay server dengan Mailcow berbasis Docker. Dengan konfigurasi ini, Anda dapat mengirim ribuan email secara aman, stabil, dan efisien, sambil mempertahankan reputasi domain yang baik. 💪

1️⃣ Persiapan Server dan Domain

Pastikan Anda memiliki:

🖥 VPS/Dedicated Server: CPU minimal 2 core, RAM 4GB+, SSD 40GB+
🐧 OS: Ubuntu 24.04 LTS
🌐 Domain aktif dengan pengaturan DNS lengkap

Setting DNS di Server SMTP Relay:

🔹 A: smtp.example.com → IP_SERVER
🔹 MX: example.com → smtp.example.com (priority 10)
🔹 PTR: IP_SERVER → smtp.example.com (atur di panel provider IP)

2️⃣ Instalasi Docker & Mailcow

# Add Docker's official GPG key:
sudo apt-get update
sudo apt-get install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

# Add the repository to Apt sources:
echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
  $(. /etc/os-release && echo "${UBUNTU_CODENAME:-$VERSION_CODENAME}") stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update

sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin -y

cd /opt
git clone https://github.com/mailcow/mailcow-dockerized
cd mailcow-dockerized
./generate_config.sh

Hostname: smtp.example.com
Timezone: sesuai lokasi

docker compose pull
docker compose up -d

3️⃣ Konfigurasi HTTPS (SSL) 🔒

Mailcow otomatis mengaktifkan SSL dari Let’s Encrypt jika domain mengarah ke server dan port 80/443 terbuka.

4️⃣ Menambahkan Domain di Mailcow UI 📨

Login ke https://smtp.example.com/admin
Masuk menu Domains → Add domain
Isi domain Anda, aktifkan DKIM (2048 bit), centang Active ✅
Tambahkan record DKIM, SPF, dan DMARC sesuai panduan di UI

5️⃣ Membuat Akun SMTP 👤

Masuk menu Mailboxes → Add mailbox
Buat username (contoh: [email protected]) dengan password kuat 🔐
Atur quota sesuai kebutuhan, centang IMAP, SMTP, dan Sieve

6️⃣ Tuning Performa & Keamanan ⚙️

Postfix:

sudo mkdir -p data/conf/postfix
sudo bash -c 'cat > data/conf/postfix/extra.cf <<EOF
default_process_limit = 200
smtp_destination_concurrency_limit = 50
smtp_destination_rate_delay = 0s
EOF'
docker compose restart postfix-mailcow

Rspamd Rate Limit (tanpa batas tapi aman):

sudo mkdir -p data/conf/rspamd/local.d
sudo bash -c 'cat > data/conf/rspamd/local.d/ratelimit.conf <<EOF
rates {
  per_user = {
    key = "user.lower";
    bucket = [
      { burst = 1000; rate = "600 / 1min"; }
    ];
    message = "Guard: minute rate limit exceeded for this user";
  }
  per_ip = {
    key = "ip";
    bucket = [
      { burst = 600; rate = "400 / 1min"; }
    ];
    message = "Guard: minute rate limit exceeded for this IP";
  }
}
EOF'

sudo bash -c 'cat > data/conf/rspamd/scores.d/ratelimit.conf <<EOF
symbols = {
  RATELIMITED = { weight = 0.0; description = "Minute guard telemetry only"; };
}
EOF'

docker compose exec rspamd-mailcow rspamadm configtest
docker compose restart rspamd-mailcow

Perbaikan MAILCOW_WHITE (jika muncul error dependency):

sudo mkdir -p data/conf/rspamd/maps.d
sudo touch data/conf/rspamd/maps.d/whitelist.map
sudo bash -c 'cat > data/conf/rspamd/local.d/multimap.conf <<EOF
MAILCOW_WHITE {
  type = "from";
  filter = "email:addr";
  map = "$LOCAL_CONFDIR/maps.d/whitelist.map";
  description = "Global whitelist (UI)";
  group = "policies";
  action = "accept";
}
EOF'
docker compose exec rspamd-mailcow rspamadm configtest
docker compose restart rspamd-mailcow

7️⃣ Pengujian SMTP 🧪

swaks --server smtp.example.com --auth LOGIN --au [email protected] --ap 'PASSWORD' --to [email protected] --from [email protected]

Atau kirim via Webmail SOGo: https://smtp.example.com/SOGo

8️⃣ Tips Keamanan 🔐

Gunakan password yang kuat 💪
Buat akun berbeda untuk setiap pengguna 👥
Pantau log secara rutin:

docker compose logs -f postfix-mailcow
docker compose logs -f rspamd-mailcow | grep RATELIMIT

9️⃣ Manfaat Konfigurasi Ini 🌟

Mampu mengirim ribuan email per menit sesuai pengaturan aman 🚀
100% open-source dan self-hosted
Mendukung multi-user 👨‍💻
Reputasi domain/IP terjaga dengan proses warm-up 🔥

Dengan konfigurasi ini, Anda memiliki SMTP relay server profesional yang aman, powerful, dan siap digunakan untuk keperluan email marketing maupun komunikasi skala besar. 🎯