how to configure multiple IMAP/SMTP domain adresses ?

[estebanlm]

Hello,
I am sorry if this is not the right place, but I have been lurking around without finding any answer...

I have docker-mailserver behind a reverse proxy, configured with a virtual host and a secondary domain, let's say mail.virtualhostdomain.comand mail.secondarydomain.com.
Each domain has a couple of email addresses.
Now, my problem is when configuring IMAP/SMTP client. If I use mail.virtualhostdomain.com it works properly for addresses in that domain AND in addresses in the secondary domain... but if I use mail.secondarydomain.com to configure a client for someaddress@secondarydomain.com, the IMAP/SMTP server is not recognized (not reachable, it says).

This is my docker compose config:

version: "3.3"

services:
  mailserver:
    image: docker.io/mailserver/docker-mailserver:latest
    container_name: mailserver
    # If the FQDN for your mail-server is only two labels (eg: example.com),
    # you can assign this entirely to `hostname` and remove `domainname`.
    hostname: mail
    domainname: domain.com
    # env_file: mailserver.env
    # More information about the mail-server ports:
    # https://docker-mailserver.github.io/docker-mailserver/edge/config/security/understanding-the-ports/
    # To avoid conflicts with yaml base-60 float, DO NOT remove the quotation marks.
    ports:
      - "25:25"    # SMTP  (explicit TLS => STARTTLS)
      - "143:143"  # IMAP4 (explicit TLS => STARTTLS)
      - "465:465"  # ESMTP (implicit TLS)
      - "587:587"  # ESMTP (explicit TLS => STARTTLS)
      - "993:993"  # IMAP4 (implicit TLS)
    volumes:
      - ./docker-data/dms/mail-data/:/var/mail/
      - ./docker-data/dms/mail-state/:/var/mail-state/
      - ./docker-data/dms/mail-logs/:/var/log/mail/
      - ./docker-data/dms/config/:/tmp/docker-mailserver/
      - ./docker-data/certbot/certs/:/etc/letsencrypt
      - /etc/localtime:/etc/localtime:ro
    restart: unless-stopped
    stop_grace_period: 1m
    environment:
      - SSL_TYPE=letsencrypt
      - VIRTUAL_HOST=mail.domain.com
      - LETSENCRYPT_HOST=mail.domain.com
      - ENABLE_SPAMASSASSIN=1
      - SPAMASSASSIN_SPAM_TO_INBOX=1
      - ENABLE_CLAMAV=1
      - ENABLE_FAIL2BAN=1
      - ENABLE_POSTGREY=1
      - ENABLE_SASLAUTHD=0
      - ONE_DIR=1
      - DOMAINS=mail.secondary.com
    cap_add:
      - NET_ADMIN
      - SYS_PTRACE
    networks:
      - server

  nginx-proxy-lorenzano:
    image: nginx
    container_name: nginx-proxy-secondary
    environment:
      - VIRTUAL_HOST=mail.secondary.com
      - LETSENCRYPT_HOST=mail.secondary.com
    networks:
      - server

networks:
    server:
        external: true

Any help is welcome :)

[polarathene]

Assuming your reverse-proxy supports the IMAP and SMTP protocols (not just HTTP/S), then you should be able to get that working correctly at least. I'm not able to assist you there as it's not something I've personally setup before for this project.

The other part with additional domains is also not something I understand well enough to advise further. My understanding is that docker-mailserver can be configured to support multiple domains, but is primarily configured as the MX mail server domain.

For example, you could have mail.example.com that doesn't handle email for hello@example.com, but does for hello@example.net and hello@example.org. So try to think of it this way as a separate server responsible for handling mail on behalf of multiple other domains.

The mail server will send from the same IP address and should have a reverse DNS (rDNS) lookup for that IP to the mail server FQDN (eg: mail.example.com). Your other domains (.net/.org) will have DNS records such as SPF which will permit mail.example.com to send mail on your behalf, and MX records that point to mail.example.com to receive mail for each domain (with mail.example.com being an A record, not a CNAME).

Hopefully that clears things up a bit better? You mail clients for IMAP (and submitting mail to send via SMTP, or rather ports 465 or 587) would connect to mail.example.com which is where your mail server is. If you wanted to setup a reverse-proxy, then the .net/.org domains could have their own mail.example.net and mail.example.org subdomains that you configure to point to the docker-mailserver container.

That should work AFAIK, but your reverse proxy must properly be configured to support those protocols, this is not usually as well supported out of the box and may require some extra configuration. I've seen users configure Traefik for this in our Github Issues, you could try reference that.