What are some alternatives?
When comparing MailScanner and Akamai, you can also consider the following products
Scrollout F1 - Scrollout is a free and easy to use anti-spam email gateway designed for Linux & Windows administrators without advanced email security experience.
CloudFlare - CloudFlare can be used by anyone with a website and their own domain, regardless of your choice in platform
Proxmox Mail Gateway - Protect mail server against spam, viruses and malware with Proxmox Mail Gateway security for businesses, government, education and non-profit organizations.
Amazon CloudFront - Amazon CloudFront is a content delivery web service.
SpamAssassin - Use this program to "Unspam" your mailbox(es).
KeyCDN - KeyCDN is a high-performance Content Delivery Network (CDN). Lowest price globally at $0.04/GB with HTTP/2 Support and free Origin Shield.