The lifelink rules function no matter what zone an object with lifelink deals damage from.
September 30, 2011 · Innistrad
A permanent with protection can't be equipped by Equipment that have the stated quality or fortified by Fortifications that have the stated quality. Such Equipment or Fortifications become unattached from that permanent as a state-based action, but remain on the battlefield. (See rule 704, "State-Based Actions.")
June 17, 2011 · Commander 2011
A permanent with protection can’t be equipped by Equipment that have the stated quality