Hi Hannah-
Thanks for the excellent question! The most common cause that emails are not being sent by your WordPress Website is that, by default, WordPress sends email unauthenticated.
This means that it lists your “from” email address as example@gmail.com, but it doesn’t log into your email account to actually send it, so many email systems will see that as a potential red flag for Spam.
You can fix this by installing a free SMTP plugin, such as WP Mail SMTP, and configuring it with your Gmail account details. Google has instructions for using your Gmail account via SMTP here.