Warning signal for an empty Subject-line in emails

I have made a mistake with this a couple of times when I'm sending emails through workspaces: I first delete the Subject thinking I'll get back to it once I've written the message, but forget to get back to it and end up sending an email without a Subject. I'm wondering if there could be a warning sign when one is about to send emails like this, which I believe would help both the admin's work and participants' experience?

I think the subject should be required - it's probably never intentional to send without subject?

That would be even better! :)

Let's make it a mandatory field. 

We have actually made this change already. Moving this to done.