I am having the exact same problem and it is causing customers to not want to view the estimate because of it saying review and pay.  This is not a cache issue.  The estimate email when in quickbooks before hitting send says Print or save.  When you open the actual email received it instead says review and pay.  The cache on your browser would not cause that change especially if it is being opened through email service and others computers/phones, etc.  How can this error be fixed?  Thanks!