First everyone fills out their EA. There's a break in the game for everyone to see the opponents EA to include Base Speed. Than everyone turns in SOPs which result in a SITREP like this:

As you can see, the game can break quite often. There were 21 breaks between the first movement and the end of the turn. Each break allows players to see everything that's happened and redo their SOP based on that new knowledge.
So if you are worried that you can't play PBEM because you have to plan out your whole turn (or half anyway), don't be. The game will break almost every impulse. You can redo your SOP quite often to account for change. Additionally, if someone accelerates you can "me too" accelerate. If someone fires heavy weapons, you can "me too" fire.
Everything's on the computer, so you don't have to keep a gameboard set up or anything.
If you're interested in playing, just give it a try. It's free, and including me, there's three moderators available.
And if you don't like all these break points, you can use conditional orders to ignore them or react to them. Such as "if my opponent accelerates, I will accelerate too. Ignore the speed change break in this case."
Or, "If my opponent turns away from me, ignore the break for course change"
