Built-in greylisting ([greylist]), with Sovite.Abuse.Greylist deciding and the greylist_entries table remembering.

A triplet (client network, sender, recipient) seen for the first time is deferred. A retry after greylist.delay, and within greylist.retry_window, passes, and the triplet then passes at once until it has gone unused for greylist.max_age. Real mail servers retry; most spam bots do not.

If the database fails, the recipient passes: greylisting must never lose mail. In a cluster whose nodes have their own SQLite databases, entries go to the other nodes (Sovite.Core.Cluster.Sync).

As a process, it deletes expired entries every hour.

Telemetry

• [:sovite, :greylist, :deferred] - %{retry_after} (seconds), %{client_network, sender, recipient}