Complex sentence: Experienced system admins for email systems should tune their mail system settings to sensible values, and the biggest delays from greylisting systems are incurred when communicating with poorly configured sending systems with retry intervals left set at several hours or more.
Split into simpler sentences: Experienced system admins for email systems should tune their mail system settings to reasonable values. The biggest delays from greylisting systems are incurred when communicating with poorly configured sender systems with retry intervals left set at several hours or more.