Your e-mail service is sending it to spam folder because sometimes they make mistakes and predict that it is spam, even when it is not.

Think of folders as file cabinets. Your email service just sent it into your spam folder/file cabinet.

Just mark it "not spam" and that will move it back to your regular e-mails folder where you can then forward it to your friend.
Do it like this:
Click next to email which will leave a check mark next to the e-mail.
Then go to the top of that page and click "not spam" or "move to in-box"
This will move it to the In-box folder/file cabinet.

This is happening a lot more lately and many people I know are saying it's become habitual so you should check the spam folder frequently because e-mails you've been waiting for could have been sent there to that folder.