Abstract The Sieve email filtering language can be used to implement email whitelisting@ blacklisting@ personal distribution lists@ and other sorts of list matching. Currently@ this requires that all members of such lists be hard-coded in the script itself. Whenever a member of a list is added or deleted@ the script needs to be updated and possibly uploaded to a mail server. This document defines a Sieve extension for accessing externally stored lists -- lists whose members are stored externally to the script@ such as using the Lightweight Directory Access Protocol (LDAP)@ the Application Configuration Access Protocol (ACAP)@ vCard Extensions to WebDAV (CardDAV)@ or relational databases.