This Minecraft mods separates explosions from the mobGriefing gamerule.
It adds a custom gamerule, mobExplosionGriefing (true by default), which makes the explosions of Creepers and Ghast Fireballs not destroy blocks.
Also, the mod introduces another gamerule, witherGriefing (true by default), which makes the explosions of Withers not destroy blocks.
This mod only needs to be installed server-side.