With the transition, all students will have email aliases in the format FirstName.LastName@st.thi.de available.
You can use these aliases to send and receive emails. The registration address remains your primary email address and cannot be changed.
On Outlook.office.com, you can view and configure the email aliases under Settings --> Email --> Compose and Reply. @thide.mail.onmicrosoft.com is an internal system address and should not be used for sending emails.