You may have a copier/scanner with the ability to send scanned documents to an email address. In most cases, it requires configuring SMTP on your scanner.
SMTP is short for Simple Mail Transfer Protocol. You can think of it like the Post Office or the UPS Store. It's the place you take your letters and packages when you want them sent to someone.
For your scanner to send a PDF to someone via email, it must send it to a SMTP server which will accept it from the scanner and then send it to the destination address.
If you don't have a SMTP server on-site (most companies don't anymore) then you'll need to use an account from a SMTP service provider like Google, SendGrid, Amazon, etc.