A client replication component of a replication system sends to a server replication component of the replication system a request to update a target email recipient list. In response to the request, the server replication component sends to the client replication component a list of hashed blocks representing the target email recipient list. The client replication component generates a list of hashed blocks representing a local email recipient list, and compares the locally-generated list of hashed blocks to the list of hashed blocks received from the server replication component to identify the hashed blocks in the lists of hashed blocks that are different. The client replication component then sends to the server replication component the blocks of the local email recipient list that correspond to the identified, different hashed blocks for updating on the target email recipient list.