Mailboxfiler has been designed from the beginning with great privacy in mind. It really was hard to decide on the plans as it plays a crucial role in the revenue generation for Mailboxfiler. When plans were finalized based on the email count, it was pretty obvious to have some kind of simple counter for users to know their usage. Of course, it took a while to implement, and we apologize for that. Our core focus was pretty mostly on scaling the system.
Usage counter is designed based on users' plans and the incoming emails over the period of time, which is 1 month. Currently, the counter is programmed based on the number of email acceptance. Emails received by the server with known addresses are only considered. When an email is rejected due to restrictions on from address, it doesn't count on your plan. We rely on our users to make sure their unique addresses provided by Mailboxfiler are guarded.
To view the current email usage, you can log in to profile settings and view the progress bar status. Though this is not a real-time progress bar, one could get an idea of their email usage. We are working hard to make sure our customers get the most out of Mailboxfiler. Please do send us your feedback.