I've got a Yahoo Mail account linked to my iphone.It is set up using a standard Yahoo settings.
  
  New eMail comes in OK & can be viewed.
  But when it is viewed in Outlook on a desktop (which deletes it from the server), it then also deletes from the iphone.
  
  Does anyone know any way to stop the iphone deleting to synchronise with the server. I only want it to download new eMail & for storage rules to be independent.
  
  This works OK for other accounts running on POP & SMTP.
  См. статью: How can my eMail be kept on my iphone after deleting from server?