Can't send emails on IPhone

Can't send emails on IPhone

I've followed correctly all the Zoho instructions about Iphone setup, but I can't send any email using Iphone. I receive emails normally, but can't send them. In my computer, using Outlook, I send and receive normally.

Does someone have any clue about what's the trouble? Maybe an alternative setup?

Additional info: I have 2 mail accounts in my Iphone (Zoho and another).