How to Send Email Alerts for Failures in Spring Boot Using Prometheus and Alertmanager

prometheus:
    image: prom/prometheus:latest
    ports:
      - "9090:9090"
    networks:
      - app_network
    volumes:
      - ./prometheus/prometheus.yaml:/etc/prometheus/prometheus.yml
      - ./alertManager/alerts.yaml:/etc/prometheus/alerts.yaml
      - prometheus_data:/prometheus

alertmanager:
    image: prom/alertmanager:latest
    container_name: alertmanager
    networks:
      - app_network
    ports:
    - "9093:9093"
    volumes:
    - ./alertManager/alertManager.yaml:/etc/alertmanager/alertmanager.yml

alerting:
  alertmanagers:
    - static_configs:
        - targets: 
          - alertmanager:9093

rule_files:
  - "alerts.yaml"

groups:
  - name: spring-boot-alerts
    rules:
      - alert: HighErrorRate
        expr: rate(http_server_requests_seconds_count{status=~"5.."}[1m]) > 0.5
        for: 1m
        labels:
          severity: warning
        annotations:
          summary: "Tax error 5xx too high"
          description: "More than 50% of the requests on the last 1 minute return error 5xx."

      - alert: InstanceDown
        expr: up{job="spring-boot-app"} == 0
        for: 30s
        labels:
          severity: critical
        annotations:
          summary: "Spring Boot instance is down."
          description: "One of the instances of the application is not responding."

      - alert: CircuitBreakerTripped
        expr: rate(http_server_requests_seconds_count{status="503"}[1m]) > 0.2
        for: 30s
        labels:
          severity: warning
        annotations:
          summary: "Circuit Breaker frequently activated."
          description: "The application is respondig with status 503 frequently, this means internal server issues."

      - alert: RateLimitExceeded
        expr: rate(http_server_requests_seconds_count{status="429"}[1m]) > 0
        for: 30s
        labels:
          severity: info
        annotations:
          summary: "Rate Limit exceed."
          description: "The NGINX return 429(Too Many Requests), this means that the tax of requests was exceeded."

global:
  smtp_smarthost: 'sandbox.smtp.mailtrap.io:2525'
  smtp_from: 'alertmanager@demo.com'
  smtp_auth_username: 'your_mailtrap_username'
  smtp_auth_password: 'your_mailtrap_password'

route:
  receiver: email-alert

receivers:
  - name: email-alert
    email_configs:
      - to: 'devs@empresa.com'
        send_resolved: true
        headers:
          subject: '[Application Alert] {{ .CommonAnnotations.summary }}'
        html: |
          <h2>[{{ .Status | toUpper }}] {{ .CommonAnnotations.summary }}</h2>
          <p>{{ .CommonAnnotations.description }}</p>
          <hr />
          <ul>
          {{ range .Alerts }}
            <li>
              <strong>Alert:</strong> {{ .Labels.alertname }}<br/>
              <strong>Instance:</strong> {{ .Labels.instance }}<br/>
              <strong>Severity:</strong> {{ .Labels.severity }}<br/>
              <strong>Starts at:</strong> {{ .StartsAt }}
            </li>
          {{ end }}
          </ul>