From what i found doing a Google search it sounds like the app isn't a good Email app at all. And the best thing to do is look for another Choice of App other than this one..
Contact customer service, *611, and tell them you need them to disable/stop the OZ Mail text messages from long code 118012222357. Note, this is not an "international" phone number. Make sure they don't go down that bunny trail.
Not sure either. All I know is when I went from a basic phone to a smartphone. I constantly got the messages. Did research, reactivated my old phone for a minute to kill off the email accounts on it and the messages quit.
Now with all the new plans, it is no longer easily feasible to activate the old device to kill the accounts.
When you call CS, be sure to go to tech support. But calling tech support requires you to call from another phone.