This guide describes how to send an e-mail as another user.
Prerequisites
Create a new e-mail
Click on the 3 dots

Click Show from (Van weergeven)

Right click the e-mail address in the from (van) field and choose Remove (Verwijderen).

Now the from (van) field is empty. You’re free to enter any e-mail address that you want to send from.
Send the e-mail.
The next time you click on from (van) the e-mail address is displayed.