Ranking content vs. reputation in inbox placement

The decision on if and how to receive a mail and where to place it, is on the receiving side (ISP). This decision is taken automatically by machines, lets call those machines "spam filters" for convenience. Spam filters make decisions not only based on quantity and quality aspects, but also based on historical knowledge, better known as "reputation". Reputation is taken from various aspects of an E-mail. This can vary from a preciously known signed header key to particular, individual and well-known misconfigurations on the sending side. Most commonly used parameters used to gather reputation are IPs and sending domains.

Which item is ranked most important in E-Mail filtering depends on multiple factors, such as the ISP you are sending to and the type of E-Mail:

• Business E-Mail, for example, can be seen as a challenge in terms of content, especially when delivering mail to small mail servers using filters such as Spamassassin that look heuristically at the content of your E-Mail.
• Mail filtered by large ISPs or filtered by more commercial spamfilters is rather ranked based on your domain & IP reputation.
• Most ISPs use a combination of different methods.