I use YAF 1.9.5.5 on DNN 05.04.02.

When users use the "Lost Password" option on the login screen, it does not work. It shows that "Your password has been sent to your e-mail address on file.". However users never receive emails.

When I login as 'Admin' and use the "Reset/Change User Password" option form Admin panel, then it works and users receive emails with their passwords.