Thanks Cory. Here are my responses to your further questions:
Q1 Yes incoming emails show a paper clip opposite the name in the email itself
Q2 That's odd, I don't see that anywhere, either in the Mail Finder field nor the OS X Finder Field.
Q2a (is Mail & Messages selected in > System Preferences... > Spotlight > Search Results?): Yes
Q3 As far as I can see, I only use the one account, (e-mail address removed)
Q4 Because of the number of Emails I receive daily, about 25 plus 20 to 30 sent directly to my Junk folder, so every 2 weeks I do a thorough clean up (deleting emails no longer required) and back up all my data files including emails to a separate hard drive. In this arrangement, "Removing attachments" and "Rebuilding" recovers quite a bit of disc space.
Q5 Thanks. I'll try that next time.