Abstract: An electronic mail (email) system may include a plurality of mobile wireless communications devices, a plurality of email storage servers, and an email aggregation system operatively connected between the plurality of mobile wireless communications devices and the plurality of email storage servers for directing emails therebetween. The email aggregation system may include an inbound gateway server for receiving inbound emails and selectively adding supplemental processing data thereto, as well as at least one mail user agent (MUA) server downstream from the input gateway server for processing received emails based upon the selectively added supplemental processing data. The email aggregation system may further include an outbound gateway server downstream from the at least one MUA server for sending outbound emails after removing the supplemental processing data therefrom.