Features to Look for in SMTP Providers. Choosing a free SMTP server is important when you’re just starting out, but there are other factors to consider beyond the price tag. Think about whether the third-party SMTP service offers: Email address validation services to improve your mailing list (because handling thousands of outgoing emails doesn’t matter much if you’re sending. Send 100 emails/day free forever. SendGrid is the world's largest email infrastructure as a service provider. We send over 100 billion non-spam emails a month for over 80,000 paying customers including technology leaders like AirBnB, Spotify, and Uber. Integrate in Minutes with our simple SMTP relay or choose from our many flexible APIs: SMTP.