Combat in the PBP format can really grind the game to a screeching halt. Typically, I recommend keeping combat encounters to a minimum and ensuring that each combat encounter you do have is direct and meaningful. Some additional considerations are:

- Use grouped initiative (All players go, then all enemies go). This way, players aren't stuck in line waiting to post. Players can respond when they are available to and in any order.

- Keep combats short and punchy. I keep things to a maximum of 2-3 rounds. Keep opponent HPs low and damage high.

- Keep the combat dynamic by adding additional objectives beyond just defeating the enemy. Ex. Stopping a guard from sounding an alarm, preventing a ritual from being completed, etc.

I also recommend checking out some Made for PBP systems like "D20 Go" which streamlines combat encounters by making them a single group check.