Alert using SMTP notifications, receiving 1000+ mails

I’m using SMTP as receiver for an alert. This worked in the passed but for the last (I guess) 2 versions it’s sending 1000s of mails a minute. Anyone else with this problem?

notify:
  - name: notify_me
    platform: smtp
    server: mail.runbox.com
    port: 587
    timeout: 15
    sender: [email protected]
    encryption: starttls
    username: !secret mail_username
    password: !secret mail_password
    recipient:
      - [email protected]
    sender_name: Home Assistant
    debug: True

alert:
  mobile_battery_low:
    name: "Mobile batterij bijna leeg!"
    entity_id: binary_sensor.mobile_low_battery
    repeat:
      - 15
      - 30
      - 60
    notifiers:
      - notify_me
  test_notify:
    name: Notify test
    entity_id: light.kaku_2
    repeat:
      - 15
      - 30
    notifiers:
      - notify_me