Which of the following will MOST likely cause major performance issues on an email server?

RAID 0 configuration, while lacking redundancy, typically provides improved read/write performance compared to a single disk or some other RAID levels, rather than causing major performance issues.

PBX (Private Branch eXchange) software manages phone calls and is unrelated to email server operations, so it would not directly cause performance issues on an email server.

A DHCP server assigns IP addresses to clients and is a network service separate from an email server's core functions; running it on the same machine would consume some resources but is unlikely to cause major performance issues specific to email delivery compared to real-time content scanning.

Anti-virus software on an email server performs real-time scanning of every email and attachment for malware, which is a highly I/O and CPU intensive operation. This constant scanning can consume substantial system resources, leading to significant delays in email delivery and overall server unresponsiveness.