First of all it will be useful for those who are using e-mail box on own domain and fighting with spam by using advanced technologies: SPF, DKIM and DMARC. By configuring the smtp server settings, the messages will be sent from your server and you will have full control over the whole sending process.
Additionally you can use third-party services to send email. The first one that comes to mind is mandrill.com, which allows you to send up to 12,000 emails per month absolutely free.
This functionality is only available for GOLD and PLATINUM plans.
You can send E-mail notifications via your own SMTP server (enter settings for your mail server: host, port, username/password).
To configure your SMTP server, go to the form settings and select "E-mail notification":
Go down, SMTP server settings, click on the slider:
Now you need to enter the settings for your SMTP server and save all the form settings:
By keeping these settings, all e-mail notifications for this project will be sent through this smtp server.