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Ways to fix Hotmail account not working on iPhone device
Cache and cookies
When we browse, our browser saves cache. This can overload the browser and create issues. Also, corrupted cache or cookies can stop the browser from working. So to prevent this you can clear your browser’s cache and cookies by going to the settings.

Internet connection
The problems can also be on your internet. The connectivity can be poor because of which Hotmail is not working. You can close the data and start it again. You can also turn on the airplane mode and close it.

Incorrect details
It is also possible that you might be entering an incorrect sender’s address which is preventing the email from sending. So make sure you are entering the correct details.

Outdated version
If you are using the Hotmail app then make sure it is updated. Outdated versions do not support and can create issues. So update your app.
https://www.usatechblog.com/blog/hotmail-not-working/

I think the version is quite old, or it’s not compatible with the mac os.