The game has the restriction on receiving gifts from friends: gifts are not added in excess of the given limit.
Energy received in gifts is not added in excess of the maximum allowed limit — 12 / 6 ea.
There’s also the restriction on keeping the gift scrolls (Healing, Lightning, Flame Shield, Seismic Shock) in the inventory — 6 ea. for each scroll type. Gift scrolls are not added to the inventory in excess of this limit.