1. A computer system, comprising: one or more processors; and one or more computer-readable media having stored thereon computer-executable instructions that are executable by the one or more processors and that configure the computer system to maintain filtering criteria for classifying electronic messages in a multi-tenant environment, including computer-executable instructions that configure the computer system to perform at least the following: maintain tenant-level filtering criteria for each of a plurality of tenants in a multi-tenant environment including, for each tenant: identifying one or more feedback signals from one or more users within the tenant regarding a messaging campaign; and updating tenant-level filtering criteria for the tenant with respect to the messaging campaign, including: when the messaging campaign has not yet been categorized, and when the one or more feedback signals indicate that the messaging campaign is undesirable to the tenant, updating the tenant-level filtering criteria to signal the messaging campaign as undesirable for the tenant; and when the messaging campaign has previously been categorized as undesirable, and when the one or more feedback signals indicate that the messaging campaign is desirable to the tenant, updating the tenant-level filtering criteria to signal the messaging campaign as desirable for the tenant; calculate a reputation score for each of the plurality of tenants; and based on a threshold number of tenants, which each have a threshold reputation score, reaching a consensus regarding desirability of the messaging campaign, update global filtering criteria to signal desirability of the messaging campaign according to the consensus.