A RAID controller works by combining multiple physical hard drives into a single logical unit. It uses various RAID levels (e.g., RAID 0, 1, 5, 10) to provide different balances of performance, storage capacity, and data redundancy. For email marketing, especially when dealing with large volumes of data, having a RAID controller can mitigate the risk of data loss and ensure that your email campaigns continue to run smoothly even in the event of a hardware failure.