We are working on e-commerce product and have decided to use SendGrid for sending our users confirmation emails. Everything was fine, users registered, emails sent, but after a week our SendGrid account was blocked without any notifications. After two support requests to SendGrid we have received email from them where they ask us to know more about our business. Our answer was very fast, but 3 days gone and no any feedback from SendGrid was received and our account still blocked.
So, be careful to use SendGrid in production - they may block your acc at any moment.