Blake,
What Daniel referred to may not work for you as you won't have AzureAD P1 in place (something that is available to State/Integrated schools as part of the MoE agreement).
I wrote about it here:
I'd have to double check, but I think the Exchange Online part of the license bundle is core for the user being active... could be wrong on this but I think I've encountered it in the past.
Given you're (presumably) not going to map your domain name to the O365 Exchange environment, the only email that would end up there is that which is addressed to the alias of student@......
onmicrosoft.com so it's not exactly 'active' in any meaningful sense.
Is your goal to stop students from trying to compose/send messages in there?
Cheers