grammaticality - Why do I instinctively want to use the present tense with a conditional?

My boss is not a native speaker of English, so he often asks me to correct his writing. The problem is, he wants me to explain why I make changes, and doesn't accept "it just sounds better that way" as an answer. Usually, I come up with some likely-sounding nonsense reasoning, but this afternoon, I just couldn't articulate why I corrected his

We might be able to figure this out from the schedules you will send us.

to

We might be able to figure this out from the schedules you send us.

I know that the version with "will" is perfectly understandable, and I don't think it is ungrammatical per se; but it just sounds better without "will", and I'd like to know why.

Edit: the current highest-voted answer answers the question "why did my boss write it with a future tense". I don't care about that. That's not my question. I want to know why the present tense sounds more natural. Is there a "rule" about this? If it's not the subjunctive (since people keep downvoting the answer which says it is), what is it?

Answer

In your sentence as amended, send is without a doubt in the present indicative tense (and it is not a conditional sentence). In English, however, the present tense does rather more than express what’s going on in the present. To talk about something that’s going on right now, we generally use be + the –ing form of the verb which describes the action or state. We use the present tense, on the other hand, to refer to:

(1) a fact that is always or generally true (Water boils at 100 degrees centigrade);

(2) a repeated action (I go to church every Sunday);

(3) an event that occurs at the moment we are speaking (I promise); and

(4) fixed or planned events taking place in the future (My flight leaves early tomorrow morning).

In your example, send could express either (2) or (4), depending on the context. In either case, it is understood that the schedules are or will be sent according to a pre-arranged plan. If that were not to be the case, you would have to say We might be able to figure this out from the schedules you’ll be sending us. Perhaps that was what your boss meant. If so, he was half right, but we express the future by using will + the plain form of the verb only when we are making a prediction or when we are expressing a decision, often made at the time of speaking, about the immediate future. Neither of those cases seems likely given the first half of the sentence.