A storage controller processes electronic messages by partitioning a storage device into logical disks and designating a logical disk as unavailable based on its storage capacity being fully used. A future time is assigned to each logical disk that is available for writing, and an estimated deletion time is determined for an electronic message. The electronic message is stored in a logical disk that is identified by comparing the assigned future times of the logical disks to the estimated deletion time of the electronic message. The electronic message is deleted based on the detection of a triggering event. If deleting messages result in an unavailable logical disk having more than a threshold amount of unused storage capacity, then each of the electronic messages stored in the unavailable logical disk is copied to a logical disk available for writing and the unavailable designation is removed from the logical disk.