Show "service unavailable" page when service is down

[manuscule]

Description
When the mail service is unavailable like today, the app redirects to the login page. I tried several times to connect via the app, which failed when submitting the sms code. Now it shows a short server error message only. Only when I tried to connect via the web, I understood that the whole service is down.

Expected behavior
Show the same error page than when accessing mail.infomaniak.com (service unavailable).