Currently, the "From" field shows the picklist (or text box, depending on your
SendEmail version), followed by "@www.mydomain.com".  I would like this to read
"@mydomain.com".  In other words, just strip the "www."

Suggest changing the source as follows:

action.defaultadmin.php, line 40:

OLD:
      @<?php echo $_SERVER['SERVER_NAME']; ?></td>

NEW:
@<?php echo str_replace("www.","",$_SERVER['SERVER_NAME']); ?></td>

Thanks!!