Deleted Email not Synchronizing with iPhone

I have Zoho mail setup on an iPhone 5 with POP settings. I do have the option called "Delete from Server" set with "When removed from Inbox". However, when I either delete email from the Zoho webmail page or delete it from the iPhone, it does not sync. In other words email deleted from the webmail page will remain on the phone. Email deleted from the phone will remain in webmail. How can I get deleted email to sync?

Thanks.