>>52291
There will be other opportunities for XP farming. You can only hold so many hellfires in your main inventory, and holding a full inventory will disrupt your ability to roll FP without checking in every 2 minutes. If you are rolling enough FP to keep up with monthly Grail casting and/or event three star CE hunting, you're going to get more hellfires than you know what to do with anyway.
Just keep buying the monthly mana prism and event shop blazes and hellfires as they are the most efficient XP per inventory slot possible at 50 to $100 per mailbox slot. Your mailbox should be optimized for the most XP per slot, and any single hellfire or stack of four or less blazes should be removed immediately and archived or burned or used accordingly. Barring that point of guidance, you should always withdraw embers and blazes in expiration order.
Stock your veteran apples or grind mats off free quests. Unless your grailing period is imminent there's no reason to be in the XP mines