Most orgs have an internal SMTP server that will accept and send mail to other internal addresses without any special authentication or validation. It's almost essential for automatic monitoring software and that sort of thing.

Where the barriers go up is at the border to the Internet. And thank goodness, just a couple decades ago it was sheer chaos.

[–] JackbyDev@programming.dev 4 points 1 year ago

I was on the school network, so maybe they accept ones from within and reject ones from outside.