A suitable nerf for orb spells?

[Gauntlet]

I agree with the above, but if you want suggestions on dealing with a Mailman without upping the ante even further:


Mirror Image is a pretty accessible spell effect which hurts ranged-touch-attack effects, and the bigger dragons should easily have enough spellcasting ability to apply it. Other similar options include invisibility, displacement, blink effects and illusions - the Orb doesn't have an exceptional range, and it costs a lot of resources to throw them out at everything, which means a few duplicates would make it such that he can't afford to throw one out until he's certain his target is the real thing.

Energy immunity options would also hurt him - while he has elemental substitution, he needs to pick the right effect for the target anyway, and if he's known to throw high damage energy effects around then Disguise Self is also highly accessible to any opponents of the caliber he's facing.

Globe of Invulnerability also stops Orbs - they're still a 4th level spell effect, regardless of the metamagic applied to them, unless they are Heightened.

Regarding other options for contributing to a fight against an enemy with good saving throws, you could summon creatures which can contribute to combat, or provide battlefield control. If you're worried about spell resistance, then spells like Assay Spell Resistance could let you get through that more easily.

If you have Shapechange access, then turning into something relevant also applies. There's a Shapechange handbook which has good options in it if you want details there, but it does basically everything.