IPhone 4S exchange emails not working?

All of a sudden my iPhone 4S has stopped receiving emails to my exchange account (work emails) however I'm getting emails to yahoo account (personal) on the same phone.
Sending emails also working strange as sometimes it doesn't work and when it does, it may take a day!
Please note that I send emails using yahoo account from mobile.

My exchange account is working ok on my laptop and iPad so I'm sure it's to do with phone or phone settings.

My battery is also draining quickly.

Few days ago, I changed the notification settings of many apps to off (to improve battery life), and I suspect that email issue started since then. Now I have put old settings but no joy. I have also rebooted iPhone, deleted exchange email account and set again, reset network settings - no luck.

Any suggestions please? Thank you in advance.

Added (1). Hawa, if this is the only option - How to backup and restore?

Back up your stuff and restore everything!

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