If you want to use Gmail SMTP in your DNN website, this can be easily done by specifying the correct port 587 in the SMTP settings. Unfortunately, there is no port number field supplied in the SMTP settings form. So in order to include the port number, you just need to add the smtp.gmail.com:587 in the SMTP settings.

In order to set the SMTP settings, you will need to login as super host account. Note this is a super administrator account so the basic administrator account will not get the access to the host menu. Under the host settings in the advanced settings tab, you will see a section for SMTP settings. You just simply need to use the following settings. Just replace the email and password of your own.