In-Memory

The in-memory lookup store is a static key value store that is kept entirely in memory. They are defined directly in the configuration file and are useful for storing small amounts of static data that do not change often. In-memory stores are used primarily by the SMTP server from expressions or Sieve filters and their contents can be defined directly in the configuration file or loaded from local files or from remote HTTP resources.

Configuration

Lookup stores are specified in the configuration file under the lookup.<name> section, where <name> is the unique identifier for the lookup store. Keys under the lookup.<name> section define the entries in the lookup store, where the key is the lookup key and the value is the lookup value.

For example, to create the allow-list-domain lookup store with the keys example.com and example.org, the configuration would look like this:

[lookup."allow-list-domain"]
example.com = true
example.org = true

It is also possible to use glob patterns in the keys to match multiple entries. For example, to create a lookup store that matches all subdomains of example.com and all mail exchangers of example.org, the configuration would look like this:

[lookup."allow-list-domain"]
"*.example.com" = true
"mx?.example.org" = true