Communications system including aggregation server for determining updated metadata of e-mail messages and related methods

A communications system includes a mobile wireless communications device and an e-mail server configured to store pushed e-mail data and metadata associated therewith already pushed to the mobile wireless communications device. An aggregation server is configured to download a first set of metadata of pushed e-mail data at a first time, and generate and store a first set of hash values corresponding to the first set of metadata. The aggregation server is also configured to download a second set of metadata of pushed e-mail data at a second time after the first time, and generate and store a second set of hash values corresponding to the second set of metadata. The aggregation server is further configured to determine an updated set of metadata based upon a comparison of the first and second sets of hash values, and push the updated metadata to the mobile wireless communications device.