[WP] Subscribe to Download plugin can't send e-mails

Hello guys,

I installed "Subscribe to Download" plugin for Wordpress. I'm able to insert short code into posts, but when e-mail is entered nothing is being send. I tried it with yahoo, gmail, and my website's domain. Nothing worked. So I can't figure out if it's wordpress' mistake or plugin's. Or mail server's.

Hope somebody will have an advice for me.

Thanks in advance!