Trigger Attachment Too Large Error Earlier

The behavior we see now: a user tries to send an email that is too large (has an attachment too close to the 100MB limit to send for O365) and when she hits send, then she gets the error after it tries.

Behavior we'd like (which mimics Outlook): Front recognizes before trying to send that the attachment is too large to send, and prompts her for a different way to send the attachment.