SMTP is a free addon powered by WPDigiPro plugin so, you don’t require any license key to use it.
It allows you to configure your mails being delivered via your SMTP instead of your server. Every hosting company provides a guide on parameters required to configure SMTP. Add the required parameters and to perform a test use the Testing and Debugging Settings provided.
Common Installation Problems
“Are you sure you want to do this?”
If you get the “Are you sure you want to do this” message when installing any .zip file via WordPress, it means you have an upload file size limit. Install the plugin via FTP if this happens, or ask your hosting company to increase the limit.