Q: This shrub is a volunteer. This year it has put out large poofs of small white blooms. The blooms have a mild sweet fragrance. What is it?
A: Since I see that emerging leaves are green and since the plant is a volunteer, I deduce that it is Chinese photinia, Photinia serrulata.
Red tip photinia, Photinia x fraseri, produces red new leaves and can not be propagated from seed. This once-common ornamental shrub was selected from seedlings of Chinese photinia.
Your Chinese photinia will probably have big clusters of red berries in summer. Birds will eat them and spread the plant further.