1. Reliability and Deliverability: Postfix is a widely used open-source mail server software that is known for its reliability and stability. It is highly configurable and can handle a large volume of emails. On the other hand, SendGrid is a cloud-based service that focuses on high deliverability rates by optimizing email sending through advanced algorithms and email infrastructure.

2. Email Automation and Marketing: SendGrid offers an extensive set of features for email automation and marketing campaigns. It provides easy integration with various customer relationship management (CRM) tools, allowing businesses to automate their email workflows and track email performance. Postfix, being primarily a mail transfer agent (MTA), does not have built-in features for email marketing or automation.

3. Email Parsing and Tracking: SendGrid offers robust email parsing and tracking capabilities that allow businesses to track email opens, clicks, unsubscribes, and other engagement metrics. It enables businesses to monitor the effectiveness of their email campaigns and make data-driven decisions. Postfix does not provide these tracking features natively, as it mainly focuses on reliable email delivery.

4. SMTP and API Integration: Postfix is generally used as an SMTP server, which means it accepts incoming emails and delivers them to the recipient's mailbox. It can also be integrated with various APIs to enhance its functionality. On the other hand, SendGrid provides a full-fledged API that allows developers to integrate email sending and tracking capabilities into their applications more seamlessly.

5. Email Deliverability Tools: SendGrid offers a range of tools and services to improve email deliverability, such as email authentication, domain reputation management, and IP warm-up guides. These tools help businesses ensure that their emails reach the recipients' inbox and avoid being marked as spam. Postfix does not provide these deliverability tools as comprehensively.

6. Pricing and Scalability: Postfix is an open-source software and can be freely installed and used on any server. It is highly scalable and can handle large email volumes efficiently. SendGrid, on the other hand, offers flexible pricing plans based on the number of emails sent, making it suitable for businesses of all sizes. It also provides scalable infrastructure to handle high email traffic during peak times.

In Summary, Postfix excels in reliability and being highly configurable, while SendGrid focuses on email automation, parsing, and tracking with advanced deliverability tools and scalable pricing options.