For the last two weeks, my Zoho Mail App on my iPhone which has worked fine up to this point has been unable to connect to the mail server.

I can't access my emails even though I will get notification banners on the screen saying that they have been received.

I can open Safari on my phone and then log in that way. This issue happens when I'm connected to wifi and on my phone data. 

I've tried deleting the app several times and reinstalling, and have updated to the latest version. But it still cannot connect.

Any solutions?