I doubt if you would ever see sentence #3 in business English. You might see examples of will (= BE willing) in such sentences as , "If you will guarantee delivery by the end of the month, I will confirm the order".In
theModern English, thesentence (2) is generally used for the meaning of (1), even though "you ARE" is not a conditionalsubjunctive mood [...]
However, in business English,
thesentence (3) is very often seen.
Retired English Teacher