docker-mailserver/docs/content/config/troubleshooting/faq.md

What kind of database are you using?

None. No *sql database required.
This image is based on config files that can be versioned.
You'll probably want to push your config updates to your server and restart the container to apply changes.

Where are emails stored?

Mails are stored in /var/mail/${domain}/${username}.
You should use a data volume container for /var/mail to persist data. Otherwise, your data may be lost.

How can I use data volume container as proposed above?

Here is a docker-compose.yml example which use a data volume container for email storage named maildata.

maildata:
  image: ubuntu
  volumes:
    - /var/mail
  command: /bin/true

mail:
  image: "tvial/docker-mailserver"
  hostname: "mail"
  domainname: "domain.com"
  volumes_from:
   - maildata
  ports:
  - "25:25"
  - "143:143"
  - "587:587"
  - "993:993"
  volumes:
  - ./spamassassin:/tmp/spamassassin/
  - ./postfix:/tmp/postfix/
  - ./opendkim/keys:/etc/opendkim/keys
  - ./letsencrypt/etc:/etc/letsencrypt
  environment:
  - DMS_SSL=letsencrypt

What about backups?

Assuming that you use docker-compose and a data volume container named maildata, you can backup your user mails like this:

docker run --rm \
--volumes-from maildata_1 \
-v "$(pwd)":/backups \
-ti tvial/docker-mailserver \
tar cvzf /backups/docker-mailserver-`date +%y%m%d-%H%M%S`.tgz /var/mail

How can I configure my email client?

Login are full email address (user@domain.com).
Both login and password are managed in postfix/accounts.cf file.
Please have a look to the README in order to manage users and aliases.

# imap
username:           <user1@domain.tld>
password:           <mypassword>
server:             <mail.domain.tld>
imap port:          143 or 993 with ssl (recommended)
imap path prefix:   INBOX

# smtp
smtp port:          25 or 587 with ssl (recommended)
username:           <user1@domain.tld>
password:           <mypassword>

How can I manage my custom Spamassassin rules?

Antispam rules are managed in spamassassin/rules.cf.

What kind of SSL certificates can I use?

You can use the same certificates you use with another mail server.
The only thing is that we provide a self-signed certificate tool and a letsencrypt certificate loader.

I just moved from my old mail server to docker-mailserver but "it doesn't work".

If this migration implies a DNS modification, be sure to wait for DNS propagation before opening an issue. Few examples of symptoms can be found here or here.
This could be related to a modification of your MX record, or the IP mapped to mail.my-domain.tld.