Since 2019/08/19, we’ve added a domain alias @cloud.nthu.edu.tw to our G Suite email @gapp.nthu.edu.tw. Here’s how it works (The following messages are rewritten from https://support.google.com/a/answer/7504451?hl=en):
You have an email address at both primary domain @gapp.nthu.edu.tw and domain alias @cloud.nthu.edu.tw.
All messages arrive in your primary domain @gapp.nthu.edu.tw mailbox.
You can reply to messages from either of your primary domain @gapp.nthu.edu.tw or domain alias @cloud.nthu.edu.tw addresses.
Google Calendar invites and sharing invites are sent only from your primary domain @gapp.nthu.edu.tw address.