mta and mda containers are creating and mounting volumes that are left uncleaned when the stack is shut down

[vrennert]

Describe the bug
mta and mda containers are creating unnamed volumes that are not cleaned up on ./bin/production.sh down

To Reproduce

docker inspect -f '{{ json .Mounts }}' mailserver-mta-1 | python3 -m json.tool
[
...tls mounts here...
{
"Type": "volume",
"Name": "dc6f64b428b30a73024db40c35bfdddd7da5e6352df42dbe9d691d9735e78959",
"Source": "/var/lib/docker/volumes/dc6f64b428b30a73024db40c35bfdddd7da5e6352df42dbe9d691d9735e78959/_data",
"Destination": "/var/spool/postfix",
"Driver": "local",
"Mode": "",
"RW": true,
"Propagation": ""
}
]

docker inspect -f '{{ json .Mounts }}' mailserver-mda-1 | python3 -m json.tool
[
...tls mounts here...
...data-mail here...
{
"Type": "volume",
"Name": "03497c577f12013d5b40fa4f6ab6733b8f390fdca4b5b7628b2d0126a194bc26",
"Source": "/var/lib/docker/volumes/03497c577f12013d5b40fa4f6ab6733b8f390fdca4b5b7628b2d0126a194bc26/_data",
"Destination": "/srv/mail",
"Driver": "local",
"Mode": "",
"RW": true,
"Propagation": ""
}
]

Expected behavior
Clean mounts/volumes or named persistent volumes if the runtime data is needed for correct functionality