Q: Do we need to include all the variables in the post to you?
A: Regarding the variables that you can omit. You can leave out "currency", and omitting the "&reply=" will just default to &reply=0". If you want to receive delivery reports including an ID is essential.
The Company Code "cc" is required as this is matched against your "eKey" (Both are case sensitive).
The rest of the variables are required.