Image not shown in newsletter using Simplenews and HTML mail

Hi all,

I am currently using my website to send out emails of newsletters when i create a newsletter content. It is a drupal 6.x version, and i had installed Simplenews, Simplenews Action and HTML mail modules.

When i sent out newsletter, i embed an image link (my website logo) to redirect to my own website. The image link is a full URL link and the code is like this:

<a href="http://www.sample.com" target="_blank"><img src="http://www.sample.com/sites/default/files/small.PNG" width="164" height="50" /></a>

However, the logo did not appear but instead showing a text URL to my website showing "http://www.sample.com". No image or broken image icon is shown. When i try to add the logo in the newsletter content by writing <img src="http://www.sample.com/sites/default/files/small.PNG" width="164" height="50" />, no image is shown too. It just give me a blank space and continue with my newsletter content.

I went to "site configuration","HTML mail" and edit the "Template" by putting the same image link in the "Header HTML" column and resend the email again. This time, the logo successfully appear in the header of email, and can redirect me to my website. But in the content, the image link still remain as a simple text link of "http://www.sample.com" and the image logo itself appear as blank. No broken image is shown although i had enable my email to show all images in the email.

I had enable the modules, checked the permission, and enable "Line break converter","URL Filter","Preformat HTML code" in HTML mail setting.

Can anyone kindly tell me what's wrong with it? This problem really troubles me. Thank you for everyone's attention.