Secure communication is of course very important for the military, so Army email is often available only via specific browsers via the army webmail.
If you are a military personnel, you can find more resources on where to login to your army mail here:
Army OWA Email Login / ARMY 365 Webmail
The Army webmail login can be accessed at this URL: https://webmail.apps.mil/mail and can be used only via Microsoft Edge or Chrome.
Source: https://www.dodreads.com/links/popular-army-web-links/army-owa-webmail/