What are some alternatives?
When comparing SpamSieve and BitNinja.io, you can also consider the following products
Mailwasher - Over 8 million people use MailWasher as their spam filter
Akamai - Akamai is the leading content delivery network (CDN) services provider for media and software delivery, and cloud security solutions.
Spamihilator - The free Anti-Spam-Filter Spamihilator removes more than 98% of spam mails before they even get into your inbox.
CloudFlare - CloudFlare can be used by anyone with a website and their own domain, regardless of your choice in platform
Spam Reader - Spam Reader is a free anti-spam add-on for Microsoft Outlook.
Scrollout F1 - Scrollout is a free and easy to use anti-spam email gateway designed for Linux & Windows administrators without advanced email security experience.