The best way to make sure that your students are using their student email addresses is by having an LTI or the SURFconext integration with Sowiso. If you don't have such an integration, you can follow the steps below to still restrict your students so that they can only create a Sowiso account by using their student email address.
Go to the Teacher tab in your class, and then to "Settings". Scroll down to "Student data" and under "Allowed domains for email registration" fill in the domain of your school.
For example, we can set up the domain to: uni.edu.com
If the student tries to log in using a different domain, they will get the following error: Email should be an allowed domain: uni.edu.com