I've done a lot of PBP/PBEM games, and tried to do games like Pathfinder via PBEM. I'm currently running a Rolemaster game by PBEM and have tried several different solutions before settling on my solution (see below)
The problem with running pathfinder as a Play By Post or play by email is the sheer number of posts required to complete a combat.
For a typical group of 4 characters and 1 GM with a fairly short 4 round combat you're looking at 9 x 4 posts (4 character posts + DM result + monster round) which is 36 posts, a massive amount of posts and delay. Even if you manage one post/day which is usually fairly good for play by Email, forum posts can be faster, you're looking at around a month to complete a combat if people post on weekends.
So Pathfinder is designed for tactical play on a board and play by post is really bad at handling that game style.
What you can do is trim down the forwards and backwards for characters by reducing what they do.
- GM Makes all rolls. This slimlines everything down a lot.
- Run characters in blocks. Usually you can run two consecutive characters actions with minimal disruption if they're just whacking the bag guy and the mob still has enough hits left to take it all.
- Run different areas in blocks. This isn't so common, but if Bob the Barbarian is on the wall attacking guards and Fred the Fighter is in the courtyard attacking guard dogs then you can get them both to reply at once.
All this will help, but you're still going to have really slow encounters.
What I suggest if you still want to run Pathfinder for combats is one of these broader solutions, while the GM makes all rolls.
Stuff initiative and have everyone declare actions at the same time. Resolve them all as sensibly as you can and then get a result from it. This cuts down a lot of time but is very complicated for the GM.
Trim out feats that are harder to use by PBP and go to mapless/descriptive. Change the play style to more descriptive and remove feats that rely more on tactical play like flanking bonuses. This isn't optimal for what you want but again can speed things up a lot.
Drag people into real time sessions to run combats. Not always an option.
Bite the bullet. You are not going to get the same tactical level of detail without significant pain in PBP, things like flanking will be harder to manage and get going; Get characters to describe what they want to do and resolve it in a more storyboard fashion giving descriptive results. Encourage players to use more descriptive terms than "I attack the orc with my +2 battleaxe" and instead encourage them to write more prose-style descriptions of combats. The joy of PBP and PBEM style play is the amount of time you can spend describing stuff and combats can become a thing of descriptive beauty. This is the option I ended up with, it takes more work and the players have to like writing but it can give great story.
TLDR: In the end, you're trying to mix a Game with a medium that it's not very compatible with and you'll have to compromise somewhere; talk to the players and see what they're prepared to give on, otherwise combats are going to be slow, tedious boring affairs.