Use PHP mail() function in docker installation with mailcatcher

I have set up a local development environment using docker compose. It consists of nginx, php-fpm, mariadb, and mailcatcher. Everything is working good, but I can't make the mail() function work.

This is my compose.yaml

version: '3.8'

services:
  nginx:
    image: nginx:latest
    ports:
      - "80:80"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf
      - ./html:/var/www/html
    networks:
      - internal
    depends_on:
      - php    

  php:
    build:
      context: .
      dockerfile: ./php/Dockerfile
    volumes:
      - ./html:/var/www/html
      - ./custom-php.ini:/usr/local/etc/php/conf.d/custom-php.ini
    environment:
      PHP_INI_SCAN_DIR: /usr/local/etc/php/conf.d      
    networks:
      - internal    

  mariadb:
    image: mariadb:10.4    
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: dbname
      MYSQL_USER: dbuser
      MYSQL_PASSWORD: dbpassword
    ports:
      - "3306:3306"
    volumes:
      - mariadb_jazdy_data:/var/lib/mysql
    networks:
      - internal

  mailcatcher:
    image: sj26/mailcatcher
    ports:
      - "1080:1080"
      - "1025:1025"    

networks:
  internal:

volumes:
  mariadb_jazdy_data:

This is my Dockerfile

FROM php:7.4-fpm
RUN curl -sSLf \
        -o /usr/local/bin/install-php-extensions \
        https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions && \
    chmod +x /usr/local/bin/install-php-extensions && \
    install-php-extensions mysqli

and this is my custom-php.ini

; Enable mysqli extension
extension=mysqli.so

[mail function]
SMTP=127.0.0.1
smtp_port=1025
sendmail_from=sender@example.com

I tried different configuration for the SMTP, including localhost, or mailcatcher. Without any success.

What am I missing here? I really would like to make this work as I literally spent hours of googling and asking chat gpt. Thanks.

I tried using different docker images, installing sendmail in Dockerfile (https://r.je/sendmail-php-docker), but nothing seems to be working.

Solution

I'm gonna answer my own question with the correct solution where Alex Howansky led me to.

However, I've made some changes also to the original compose.yaml, where I forgot to add the network directive under mailcatcher. But later, I found out, it didn't have to be there, at all.

So these is the final configuration how I made it work.

compose.yaml

version: '3.8'

services:
  nginx:
    image: nginx:latest
    ports:
      - "80:80"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf
      - ./html:/var/www/html    
    depends_on:
      - php    

  php:
    build:
      context: .
      dockerfile: ./php/Dockerfile
    volumes:
      - ./html:/var/www/html
      - ./custom-php.ini:/usr/local/etc/php/conf.d/custom-php.ini
    environment:
      PHP_INI_SCAN_DIR: /usr/local/etc/php/conf.d          

  mariadb:
    image: mariadb:10.4    
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: dbname
      MYSQL_USER: dbuser
      MYSQL_PASSWORD: dbpassword
    ports:
      - "3306:3306"
    volumes:
      - mariadb_jazdy_data:/var/lib/mysql    

  mailcatcher:
    image: sj26/mailcatcher
    ports:
      - "1080:1080"          

volumes:
  mariadb_jazdy_data:

Dockerfile

FROM php:7.4-fpm
RUN apt-get update && apt-get install -y build-essential software-properties-common
RUN apt-get install -y libsqlite3-dev ruby-dev
RUN gem install mailcatcher
RUN curl -sSLf \
        -o /usr/local/bin/install-php-extensions \
        https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions && \
    chmod +x /usr/local/bin/install-php-extensions && \
    install-php-extensions mysqli
RUN mv "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini"

custom-ini.php

; Enable mysqli extension
extension=mysqli.so

[mail function]
sendmail_path=/usr/bin/env catchmail --smtp-ip mailcatcher --smtp-port 1025