How to set Path for "img src" tag?

If you used newsletter module alone, it will send plain text to the user. How ever you put any code it will translate into plain text and user will see the code. You need to use support plugin which name Mimemail Newsletter.

I already used in my website portal. But currently it still under development. Some bugs may occur if you used comment notify but you can solve by setting in mimemail setting by checked the option of "send all email in plain text". This option don't effect the newsletter sending mail.

Then just type your newsletter by putting all the img and this module will automatically convert in coding content type. Not plain text anymore. Adios.

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this might be usefull

$url_Path = "http://".$_SERVER['HTTP_HOST'].base_path()."/files/subfolders";

Try this variable

$path=$GLOBALS['base_url']."/files";

Why don't you try the simplenews & simplenews template modules. Which is very wonderful for newsletters.

Regards,
ABC

use

drupal_get_path('module/theme')

for further defination viti: api.drupal.org