Sieve: Extlists Extension

The extlists extension (RFC 6134) enables Sieve scripts to check membership of a value in an external list or for redirecting messages to an external list of recipients. An "external list" is a list whose members are stored externally to the Sieve script. This extension adds a new ":list" match type to apply to supported tests and it can be be used to implement email whitelisting, blacklisting, addressbook lookups, and other sorts of list matching.

For Dovecot, the external list is always implemented using a dict lookup. Redirecting messages to a list of recipients as described in the standard (RFC 6134) is currently not implemented in Dovecot and will always trigger an error if used.

Configuration

The extlists extension is not available by default and needs to be enabled explicitly by adding it to sieve_extensions.

Settings

sieve_extlists_list

Default	[None]
Value	Named List Filter
See Also	Sieve extlists extension

This named list filter creates a new list definition for the ":list" match type in Sieve (extlists extension). The filter name refers to the sieve_extlists_list_name setting. That is the name of the list as it will be accessible from the Sieve. A dict definition that is placed inside the scope of this list filter will serve as the lookup for this extlists list. So, values from Sieve are looked up in the defined dict. This is often used to define an address book or whitelist external to the Sieve script. If no dict is present, the list will function as an empty list.

Example:

sieve_extlists_list :addrbook:default {
  dict proxy {
    name = addressbook
  }
}

sieve_extlists_list_max_lookup_size

Default	1k
Value	size
See Also	Sieve extlists extension

The maximum size of a value looked up from this Sieve extlists list. If the value is too large, the lookup will be skipped and will yield no result. Note that individual lists may have different limits, meaning that lookups in other lists may still succeed.

sieve_extlists_list_name

Default	[None]
Value	string
See Also	Sieve extlists extension

The name of the list as it will be accessible through the Sieve ":list" match type (extlists extension). According to the standard, this name must be a valid URI. This implementation further limits that to a valid URN or TAG URI. Note that the standard URN and TAG equality rules dictate that at least parts of these URIs are case-sensitive, so it is best to consider the configured name case-sensitive entirely.

The sieve_extlists_list filter refers to this setting.

Example

# Use extlists
sieve_extensions {
  extlists = yes
}

# No value looked up from a list may exceed 512 bytes, or it will forcibly not
# match
sieve_extlists_list_max_lookup_size = 512

# The default addressbook stored in a proxied dict
sieve_extlists_list :addrbook:default {
  dict proxy {
    name = addressbook
  }
}

sieve_extlists_list tag:example.com,2025-02-26:BadFileExts {
  dict proxy {
    name = bad_file_extensions
  }

  # Limit lookups to 10 bytes
  max_lookup_size = 10B
}

Sieve Example

The following example excludes senders listed in the user's default address book from Spam filtering. The example demonstrates the use of the spamtest extension as well.

require ["envelope", "extlists", "fileinto", "spamtest",
         "relational", "comparator-i;ascii-numeric"];

if allof( not envelope :list "from" ":addrbook:default",
	  spamtest :value "ge" :comparator "i;ascii-numeric" "3" ) {
  fileinto "spam";
}