If you are unable to claim the gems from Kamazon daily mails, this is likely due to having over 3000 stamina. In Guardian Tales, stamina cannot exceed this amount. In order to claim more mail, and thus gems, you will need to use your currently existing stamina so that you are under this limit again.
We are glad to share a quick way to quickly use all 3000+ of your existing stamina to resolve this issue:
In Heavenhold there is a building called the Guardian Base Camp. As you progress through Guardian Tales' storyline, you will unlock this facility and gain access to Guardian Levels. Once you reach Guardian Level 26, obtained after clearing World 3, you will unlock the ability to Sweep Resource Dungeons.
WHAT IS SWEEP?
Sweep is a feature that allows you to instantly obtain the rewards from a dungeon without having to manually or auto-battle through it. In this case, it will allow you to consume all 3000+ stamina that is hindering your ability to claim more mail in under 1 minute. If you encounter issues using the Sweep function, please see the following article HERE.