I love my 20" mid 2007 iMac running El Capitan (version 10.11.6). However about two weeks ago all of a sudden I can no longer share photos that I took via Apple Mail. When I called Apple, they said that my OS no longer supports sharing photos, even as attachments. The iMac cannot be upgraded any more. I am not planning to put thousands of old photos on iCloud. They said I should buy a new computer with OS no earlier than Big Sur (version 11). I want to continue to use a 20" desktop because I have an oak computer desk with a monitor space that size (non adjustable). I believe that the last 20" desktop is a late 2009 that can run High Sierra. High Sierra is the earliest OS for which Apple still gives directions for sharing photos via email. My questions: What are reputable businesses that sell refurbished imacs? How much memory could I put on the late 2009 iMac? How long would you expect that High Sierra will be viable for normal, personal interest, text writing, photo sharing use?