Sendgrid is a way to run email marketing campaigns. To run a campaign with Sendgrid through Housebuilder Pro you need to have a Sendgrid account.
API Key:
If you put your accounts’ API key into the API box you’ll be able to connect your accounts here. This means the messages sent from Housebuilder Pro can be sent out to all those customers in your database.
Default Email:
Here you can put in your email address that will send the email to customers. This is who the customers will receive their email from. These will need to be added as senders in Sendgrid. You can find information regarding this from Sendgrid here https://docs.sendgrid.com/ui/sending-email/senders.