Hi there, Pulto.
I see that you're not able to send or receive emails from an Exchange Server account while your iPhone is connected to a Wi-Fi network. You have to use cellular data in order for it to work, and I'm glad to help.
If you can’t send or receive emails on your iPhone, iPad, or iPod touch -- First, follow the steps under "Remove your email account and set it up again".
Set up Exchange ActiveSync on your iPhone, iPad, or iPod touch -- Then re-add the account using the steps in this article. You may need to contact your email provider to make sure your settings are correct.
If you set up your account correctly, or you’re still having problems, follow all of the steps provided in the first article that was shared.
Take care.