In recent years, many major ISPs such as Gmail, Verizon Media (AOL, Yahoo, Verizon) and Outlook domains have begun to take engagement into consideration for inbox placement. Because of this, senders cannot necessarily rely on seed list results alone to determine inbox placement as the insights gained from seed testing may not present a complete picture of how successful an email campaign was.

Because the email addresses in seed lists are test accounts, there is no engagement associated with them. As a result, ISPs see these accounts as inactive. Emailing to an inactive account can affect a sender’s IP/ domain reputation and can result in heavy spam foldering. This can also add another layer of complexity when warming up new IPs. Since Gmail expects senders to start with really low volume during the first couple of weeks of ramping up email sending, hitting a relatively large number of inactive addresses will complicate building a good reputation on new IPs. We always recommend that our customers send traffic to their most engaged users for the first 4 weeks of a ramp up.

Our recommendation is to avoid using seed lists during the warm-up period. And, if you decide to use seed lists after you have established a solid reputation with the ISPs, then use them as one of many other factors to determine whether or not your campaigns are successful.

Monitoring open rates can provide more accurate data points when determining whether your emails are making it into the inbox. Of course, the open rate may vary based on the type of traffic (welcome, transactional, marketing) but the average open rate for Marketing emails is about 20%, this rate is higher for transactional traffic or triggered messages.

Email testing and validation have become increasingly sophisticated since email's early days. To learn more about email's fascinating evolution and surprising statistics, check out our 13 fun email facts you might not know.