Where is mail test button?

I recently sent an invitation to 2 new staff members of our Ghost site. One got it, one didn’t. While debugging this problem, I notice that the mail “test” function is missing from the labs page as described in this article. I’ve looked all over, and cannot find it. Where is it?

This is a self-hosted installation on Digital Ocean, running Ghost v16.15.0.

That’s for newsletters, transactional email is set in the config file. If you’re using Mailgun for transactional email, visit your Mailgun console to view logs etc.