Email reception, storage, and access are very I/O-intensive processes.
Both the LDA and the MTA contribute to email peformance when delivering email. The POP and IMAP daemons contribute to email performance when email is being accessed.
For large message stores, some form of RAID system will probably be necessary. RAID Levels 1 and 0+1 are best for relatively small volumes. RAID 5orRAID 50 is usually most appropriate for very large message stores. Good hardware RAID is usually superior to software RAID, and is mandatory when running RAID 5.
Small, fast disks usually are best for email applications, especially if the email is stored transiently.
Good RAID systems can be very difficult to find. There is no substitute for rigorous testing.
