The principles of the present invention provide for categorizing electronic messages based on trust between electronic messaging entities. Messaging servers maintain trust lists indicating levels of trust between electronic messaging entities. Trust lists can be generated from existing trust information, such as, for example, address book entries. Messaging servers also maintain activity stores that indicate messaging activity between messaging entities. Based on information in a trust list and, when appropriate, information in an activity store, a messaging server can categorize an accessed electronic message, such as, for example, as unwanted and/or unsolicited. Messaging servers can securely exchange trust list information to increase the possibility of identifying a level of trust between messaging entities, even between messaging entities that have not previously exchanged electronic messages. Exchanged trust list information increases the possibility that a messaging server will be able to appropriately categorize an accessed electronic message.