Allow self-hosters to blacklist some spammers DNS domains in Rspamd

Summary

Allow self-hosters to blacklist some email domains in Rspamd, similar to whitelist.

Description

What is the current behavior?

Sometimes, Bayesian and fuzzy filters are not enough. One may need to blacklist a spammer DNS domain.
It is allowed to whitelist some domains as senders, why not also allow to blacklist some ?

What is the improved behavior?

Self-hosters could simply blacklist a spammer DNS domain.

What does it bring?

Quickly & easily put an end to some spammers.

Examples

Adding the following code to /mnt/repo-base/config/mail/rspamd/multimap.conf:

BLACKLIST_SENDER_DOMAIN {
    type = "from";
    filter = "email:domain";
    map = "/etc/rspamd/local.d/blacklist.sender.domain.map";
    score = 99.0
}

Then create a /mnt/repo-base/config/mail/rspamd/blacklist.sender.domain.map.

BTW, change files owner to allow modifying them from Rspamd web interface:

chown 107:109 /mnt/repo-base/config/mail/rspamd/*list.sender.domain.map

Finally, add this to /mnt/repo-base/docker-compose.yml, in mailserver volumes:

- /mnt/repo-base/config/mail/rspamd/blacklist.sender.domain.map:/etc/rspamd/local.d/blacklist.sender.domain.map

then recreate mailserver container.

Validation

For example, for the "OffreEntreprises" french spammer:

• get real DNS domain from emails: e.offre-entreprises.fr
• add it to blacklist file:
  
  😄 note: admin is now enable to "Write" both lists from Rspamd web interface
• gotcha!
  

Checklist

• [N/A] License
• [N/A] Translations
• [ToDo] Documentation
• Test plan