What is the ruling on a husband having intercourse with his wife during the daytime in Ramadan out of ignorance, and what is the ruling on semen being discharged merely by greeting her and continuing the fast?

If a fasting person intentionally engages in intercourse, knowing it invalidates the fast, but is ignorant of the obligation of expiation, then the major expiation is binding upon him. As for the emission of semen, it invalidates the fast and necessitates only making up that day without expiation.