I'm using sendgrid.
Just go to mail tab and fill it like that:
Driver: smtp
Host: smtp.sendgrid.net
Port: 465 (Use 587 or 25 if non SSL)
Encryption: SSL (Type TLS if non SSL)
Username: apikey
Password: generated one
Sender address: anything@yourwebsite.com
PS: Make sure that ports are correct, sendgrid says it on the page.
PS 2: Use SMTP Relay option instead of WebAPI.
