I am sorry to admit that I've never even tried play by post. How does it work? Are their any customs one should know about before trying it?
Essentially, each player posts one or more things, roughly in an informalized turn system.
1) Some in-character text (perhaps what the character is thinking or saying)
2) Any applicable information related to abilities, skill checks, etc. that the character would like to attempt
3) Any relevant out of character questions.
Each player plays roughly in turn making sure that everyone gets a chance to post before the DM advances the story.
I don't think there are any hard or fast rules (other than the ones your DM might set). The only real requirement for games played by post is patience - these games are inherently slower given the medium.
Plenty of sites have PbP forums where you can see a good example of what a game thread looks like. Hope this helped.
M|F