(Old Version) Set up a custom SMTP
Setting up a custom SMTP to send email can be done in the Settings of your inbox.
SMTP Address: smtp.sendgrid.net
SMTP Login: should be your login account to sendgrid
SMTP Password: should be your password to your account
SMTP Authentification: can be left to Default
Don't forget to click Save at the top and you are good to go.
For more information, see SendGrid documentation