Im FAQs doc:
I just installed PHPlist, but sending my first messages fails. Why can't I send any message?
* Please check if PHPlist is still running in Test mode. In config.php check your value for this constant (0 is off, 1 is on): define ("TEST",0);
Im troubleshooting doc:
Warning: Things will work better when PHP magic_quotes_gpc = on. The PHP setting magic_quotes_gpc∞ needs to be enabled for the smooth functioning of PHPlist. There are several possible ways to fix this. First you could check in the /lists/.htaccess file that it includes the line php_flag magic_quotes_gpc on. If not, try adding this line to see whether it fixes the problem. Alternatively, if your server runs PHP as CGI (PHPsuExec), you can try to enable magic_quotes_gpc by creating the file '/lists/php.ini' and adding this directive: magic_quotes_gpc = 1. If you're on shared hosting account, you can also contact your ISP to fix this.