you can use a fake webmail for catch your emails from
a smtp docker server. Like mailtrap.io

first of all, you need use the image:eaudeweb/mailtrap
in your docker-compose file.

Then you can config the mapping of ports and the enviroments
variables for access.

As follow:

 mail:
    container_name: sys_mail
    restart: unless-stopped
    image: eaudeweb/mailtrap
    ports:
      - "8125:80"
      - "2525:25"
    environment:
      - MT_USER=mailtrap
      - MT_PASSWD=mailtrap
      - MT_MAILBOX_LIMIT=512000001
      - MT_MESSAGE_LIMIT=102400001
    networks:
      orion-office-network:
        ipv4_address: 172.16.4.3

Very important your address network! because
your enviroment variable for you should be the address of your container address:

this

###> symfony/mailer ###
MAILER_DSN=smtp://172.16.4.3:25?verify_peer=0
###< symfony/mailer ###

you can acces to the admin-panel in :

172.16.4.3:80

user:mailtrap # MT_USER enviroment variables
pass:mailtrap # MT_PASSWD enviroment variables

Other important thing is the ?verify_peer parameter
by default with value true.

if you have problems with the TLS Peers, you can
disabled only for debug . TLS Peer verification

Thanks friends of Eau de web