I have to agree on the maps for any type of combat tactical/strategy situation. For email or post/web games it cuts out on any misunderstandings of the description and you dont have to spend as much time either altering a players stated action to fit or playing email/post tag telling them they cant do such and such.
Dice rolls theres two ways to go about it, you can have the players roll sets of each die type and have them take it tot he end of each message they send, say 4 rolls each of d4,d6,d8,10,d20 or you can just do it all on your side.
Doing it yourself is the method I prefer as sometimes players forget to send rolls in with a message and you can fudge however you like and no one will know at all
Anyhow the maps dont have top be pretty, I used to do simple graph paper style mapping and used numbers for each player and Letters with numbers for the baddies/npc's. You can use say windows default ms paint and make yourself a graph paper template bmp and then when you map things out save it as a jpg to send along with email so its nice n small. Allows you to make them pretty fast and for each player with only whats in their line of site and so forth.
A handy thing to do after the first couple of situations the group gets into and they have gotten their pecking order figured out, scouts, flanksers, rear guard type stuff is make some type of image on a road in the woods showing where everybody is during normal marching, so when you do wandering encounters or they stumble into a set encounter you can set the encounter up around it and theres no question of whose where, the only thing that might change is the scouts coming or going or flanking and such not. As characters, group npc's/hirelings come and go or die and get replaced its easier to shift the marching positions around. Visuals like that help a lot in setting up encounters to, makes it easier on you when typing up the initial encounter text.
If everyone has web access and not just email access you should look at
www.rondaksportal.com and set up your campaign there. Very nice play by post site, you can store lots of info right online there, postings can be broke down by players or groups(for those times the party is split up), private messages, as its own built in dice roller so oyu know the players arnt fudging, you get some web space for your campaign. You can insert images right into posts. Very friendly for play over the web. Build your own char sheets with a few prebuilt fields based on game rule type. Check it out, lurk in a few games, you might like it over trying to play by email.