The lifelink rules function no matter what zone an object with lifelink deals damage from.
April 1, 2011 · Duel Decks: Knights vs. Dragons
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.")
February 4, 2011 · Mirrodin Besieged
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.”)
October 1, 2010 · Scars of Mirrodin
A permanent with protection can’t be equipped by Equipment that have the stated quality
February 1, 2010 · Worldwake
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.")