Why could Kafka warn “partitions have leader brokers without a matching listener”?

As stated in the comments to your question the problem seems to be with the advertised name for the Kafka broker. According to your docker-compose you should be using 192.168.23.134 but your email-service is using kafka:9092. You can try with this docker-compose. I replaced the wurstmeister services with the latest Zookeeper and Kafka provided by confluentinc and added your email-service.

---
version: '2'
services:
zookeeper:
    image: confluentinc/cp-zookeeper:latest
    environment:
    ZOOKEEPER_CLIENT_PORT: 2181
    ZOOKEEPER_TICK_TIME: 2000

kafka:
    image: confluentinc/cp-kafka:latest
    depends_on:
    - zookeeper
    ports:
    - 9092:9092
    environment:
    KAFKA_BROKER_ID: 1
    KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
    KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://kafka:29092,PLAINTEXT_HOST://localhost:9092
    KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT
    KAFKA_INTER_BROKER_LISTENER_NAME: PLAINTEXT
    KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1

email-service:
  build: ./email-service
  environment:
   SPRING_KAFKA_BOOTSTRAPSERVERS: kafka:29092
  ports:
   - "8081:8081"
  depends_on:
   - kafka

advertised.listeners: Listeners to publish to ZooKeeper for clients to use, if different than the listeners config property. In IaaS environments, this may need to be different from the interface to which the broker binds. If this is not set, the value for listeners will be used. Unlike listeners it is not valid to advertise the 0.0.0.0 meta-address.

Please note that KAFKA_ADVERTISED_HOST_NAME has been deprecated and it’s recommended to use KAFKA_ADVERTISED_LISTENERS instead. For more information about KAFKA_ADVERTISED_LISTENERS check here.