The work I have been doing for a summer internship has led to me use a couple mail functions, ex: MailMessage and Mail (C# and PHP respectively). A couple sources online have mentioned that C# needs credential verification to send from an email address. In the PHP files where I used the mail function, I never had to supply credentials. I was wondering if there is normally a mail verification service that emails have to go through before getting sent out on the companies network? There must be security blocking people from using mail functions with any email they want, but what is the typical way of doing this?

This is just out of curiosity from seeing discussions in other threads. No specific help on a problem I am facing. Nothing on the PHP and SMTP websites was standing out as helpful so I thought I would ask here. Thanks!