Overview

Lookup lists serve a similar role to in-memory stores such as Redis, but with one key distinction: they are read-only at runtime. They hold key-value pairs that remain unchanged during server operation and are well suited to cases where a fixed set of values is consulted from configuration expressions or scripts.

The primary way to interact with lookup lists is through expressions, using specialised functions such as key_get, counter_get, and others. These functions allow administrators to query values from the lists and evaluate configuration dynamically based on predefined key-value pairs.

Stalwart supports both local and remote lookup lists:

• Local lookup lists are held as records managed through the MemoryLookupKey and MemoryLookupKeyValue objects. They are suitable for cases where all key-value pairs are known in advance and managed directly by the administrator.
• Remote lookup lists are fetched over HTTP and defined through the HttpLookup object. They are useful in dynamic environments where configuration is managed centrally or updated independently of the server.

Additionally, the StoreLookup object exposes an external data store as a lookup namespace, which is convenient when an existing database already holds the data the server should consult.