Simple String Replace Question

I would like to get rid of \n characters unless there are two or more in a row. So for example if there is a long email formatted like we do here with line break I want to remove the line breaks so text can be wrapped by a browser, but also show paragraph breaks where necessary. This is what I have: $string_new = str_replace("\n", "", $string); How can I augment this to not replace: \n \n Thanks. Jeff Oien