Known senders module

The known_senders module maintains a Redis-backed set of hashed sender addresses for a configured set of domains. It lets you:

• mark messages from previously seen senders as known
• flag first-time senders from those domains
• verify inbound replies using data produced by the replies module (global and per-sender local checks)

Requires Redis; optional support for RedisBloom.

How it works

1. For SMTP and MIME From addresses belonging to the configured domains, Rspamd hashes the full address and checks storage:
   • with use_bloom = false: a Redis ZSET named by redis_key
   • with use_bloom = true: a RedisBloom filter named by redis_key
2. If found, Rspamd inserts symbol (default KNOWN_SENDER). If not found, it inserts symbol_unknown and stores the sender, trimming to max_senders.
3. If the replies module is enabled, two additional checks are available:
   • symbol_check_mail_global: sender exists in the global replies set
   • symbol_check_mail_local: at least one of current recipients exists in the sender’s local replies set

Result options indicate which key matched, e.g. smtp:<hash> or mime:<hash>.

Configuration

Add configuration to /etc/rspamd/local.d/known_senders.conf (or configure Redis globally):

known_senders {
  enabled = true;

  # Redis (can be configured globally as well)
  #servers = 127.0.0.1:6379;

  # Domains to track senders (map or list)
  domains = "https://maps.rspamd.com/freemail/free.txt.zst";

  # Storage
  use_bloom = false;           # requires RedisBloom if true
  redis_key = "rs_known_senders";
  max_senders = 100000;        # max elements kept in set/filter
  max_ttl = 30d;               # default 30 days; applies to non-Bloom (ZSET) storage

  # Symbols
  symbol = "KNOWN_SENDER";
  symbol_unknown = "UNKNOWN_SENDER";
  symbol_check_mail_global = "INC_MAIL_KNOWN_GLOBALLY";
  symbol_check_mail_local = "INC_MAIL_KNOWN_LOCALLY";

  # Replies-related (must match settings in the replies module when changed)
  sender_prefix = "rsrk";
  sender_key_global = "verified_senders";
  sender_key_size = 20;        # applies to global reply-set keys only; local keys are always 8 chars
  max_recipients = 15;         # recipients to verify for local set

  # Optional privacy for reply sender before hashing
  reply_sender_privacy = false;
  reply_sender_privacy_alg = "blake2";
  reply_sender_privacy_prefix = "obf";
  reply_sender_privacy_length = 16;
}

Symbols

The module registers the following symbols with hard-coded default scores:

Symbol	Option	Default score	Meaning
KNOWN_SENDER	symbol	-1.0	sender already known
UNKNOWN_SENDER	symbol_unknown	+0.5	first-time sender stored now
INC_MAIL_KNOWN_GLOBALLY	symbol_check_mail_global	-1.0	sender verified by global replies set
INC_MAIL_KNOWN_LOCALLY	symbol_check_mail_local	-1.0	at least one recipient verified by the sender’s local replies set

Override these scores in your metrics configuration as needed.

Requirements

• Redis: configure Redis servers globally or per-module, see Redis configuration
• RedisBloom (optional): required if use_bloom = true. Enable in Redis, e.g. in redis.conf:

loadmodule /path/to/redisbloom.so

Notes

• If you change sender_prefix in local.d/replies.conf, change it here as well to keep sets aligned.
• domains accepts the same map forms used elsewhere (file/HTTP/HTTPS, compressed maps, etc.).
• sender_key_size (default 20) controls the length of the global reply-set key only. Local per-sender reply-set keys are always truncated to 8 characters regardless of this setting.