using Built in newsletter mails

when I use Built in newsletter mails and send the massage to users, in yahoo all images send as attachment in massage, and this cause bad quality of the massage, how can I avoid this[attachment=6659:massage from my site.PNG]

in other sites no attachment and the images saved in there site

[attachment=6660:massage from other site (no attachment).PNG]

massage from my site.PNG

massage from other site (no attachment).PNG