Social Booth uses Sendgrid for email delivery. You will need to signup here. It's free for 200 emails/day. If you need more there's a plan for $10/month that gives you 40k emails/month.
1. Enable Email
Checking this will enable the email sharing button for users to email their photos.
2. Sendgrid Username
This is the username that you signed up for Sendgrid with.
3. Sendgrid Password
This is the password for your Sendgrid account.
4. From Email
This is the email address that you want the emails to come from when they are sent to the users.
5. Email Subject
The subject of the sent email.
6. Email Message
The body of the email message sent to the user. You can use some basic HTML like <b>, <i> etc.