This repository demonstrates a question. To see the undesireable behaviour execute the following commands
# Start the services
docker-compose up --force-recreate --detach --build
sleep 1
# Instruct the client to send an email to [email protected] through postfix (configured by client/msmtprc)
# Should result in message "Dec 06 22:24:05 host=postfix tls=off auth=off [email protected] [email protected] mailsize=66 smtpstatus=250 smtpmsg='250 2.0.0 Ok: queued as 21B023DD17' exitcode=EX_OK"
docker exec postfix-dovecot-lmtp-reproducer-client-1 sh -c 'echo test | msmtp [email protected]'
docker exec postfix-dovecot-lmtp-reproducer-postfix-1 postqueue -p
The email will be stuck in the queue, with the message "(Host or domain name not found. Name service error for name=dovecot type=A: Host not found, try again)"
The root cause can be traced to the entry virtual_transport in postfix/main.cf. When this is changed to the ip adress of the dovecot service (probably 172.18.0.3), then it will work