Question 1

How to fix rspamd Bayes 'Missing bytes in input' error caused by expand_keys in docker-mailserver?

Accepted Answer

Set `expand_keys = false` in rspamd's `redis.conf`. The default DMS configuration enables `expand_keys = true`, which corrupts binary msgpack data in EVALSHA calls for per-user Bayes classification. Override the setting via `user-patches.sh`: create a custom `redis.conf` with `servers = "127.0.0.1:6379"; expand_keys = false;` in `/path/to/config/rspamd/local.d/`, then copy it during startup. Example user-patches.sh snippet:
```bash
if [ -d /tmp/docker-mailserver/rspamd/local.d ]; then
  cp /tmp/docker-mailserver/rspamd/local.d/* /etc/rspamd/local.d/
fi
```
This resolves classification failures and silent data corruption. Track rspamd issue #5904 for a permanent fix.

Question 2

Why do I get 'File A or B or C does not exist' when using SSL_TYPE=self-signed in docker-mailserver?

Accepted Answer

This error means one or more required certificate files are missing. When using SSL_TYPE=self-signed, docker-mailserver expects all three files: cert.pem, key.pem, and ca-cert.pem (or the custom names you configured) in the SSL directory (default: /etc/docker-mailserver/ssl/). Ensure all files exist with correct permissions. The error message is ambiguous and may be improved in the future to explicitly list missing files.

Question 3

How to set up DNS caching to avoid DNSBL rate limits on a mail server?

Accepted Answer

Deploy a dedicated DNS caching service (e.g., CoreDNS or k8s-dns) as a container alongside your mail server. Configure it to forward queries to a public resolver like Google (8.8.8.8) or Cloudflare (1.1.1.1) and enable caching. Then point your mail server's DNS to this cache (e.g., via /etc/resolv.conf or rspamd configuration). Example CoreDNS Corefile:

.:53 {
    forward . 8.8.8.8 1.1.1.1
    cache 600
    errors
    log
}

This reduces repeated DNSBL lookups and avoids rate limiting. For Docker Mailserver, see docs on RBLs: https://docker-mailserver.github.io/docker-mailserver/v15.1/config/security/rspamd/#rbls-real-time-blacklists-dnsbls-dns-based-blacklists

Question 4

How can I use Haraka instead of Postfix in Docker Mailserver?

Accepted Answer

DMS does not officially support Haraka. You can extend the DMS image to include Haraka as an additional service alongside Dovecot. Example: use a custom Dockerfile with `dockerfile_inline` in your compose.yaml to install Haraka (see https://github.com/docker-mailserver/docker-mailserver/issues/4659#issuecomment-xxxx). Then configure Haraka to listen on a separate port or relay to Dovecot. This is a self-supported customization.

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