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This page is based on a customer's question:

How would you say the switching up of content plays into hitting the inbox? As we think about open rates I’m wondering where should we rank this.


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.

Did you know?

Only with a valid DMARC record can your domain's reputation properly be measured.

It's impossible to make a definite statement as to what is more important, or higher ranked. Boiling it down to the essence, it all falls back to the old adage, send frequent, relevant and consistent content, build on top of a good reputation, use qualified E-Mail templates and avoid spammy phrases or shouting language. In order to keep engagement rates up it is good to keep A/B-testing new content to see what works best with your recipients. It's always recommended to test your configuration, content, reputation and inbox placement rates with InboxSys.