Open rates dropped drastically in a short period of time

Hi everyone! I have an odd situation and I'm wondering if anyone else has experienced this and has some insight.


My organization began using BBNC to deploy a monthly newsletter (among other emails) in January 2018. Our open rates were continually improving, reaching their highest total (approx 20%) over the summer. In October we had an 18% open rate. Then in November our open rate dropped to approx 10% and stayed there for December and January. Our February open rate dropped again to 6%. A similar trend started occurring with a weekly email we send out, except those open rates started dropping at a later time (around January). During this time, we did not change the day of the week that we send these emails on.


While I know a drop in open rates could be related to a drop in readership, we have never seen such low figures before. Prior to using BBNC, we used another deployment system where we averaged a 15% open rate, often times higher. I pulled a list of constituents who opened the newsletter in October 2018 and then stopped opening, but I'm not seeing any patterns or similarities among those email addresses (in terms of domain, soft bounces, etc). We removed hard bounces from our lists, but so far that hasn't seemed to improve things. Some constituents who are no longer opening the newsletter do sometimes open other types of emails we send and do open emails from other departments in our organization (which use a different sender email name and address). I contacted BBNC support but they said between October 2018 and now nothing has changed in regards to what they define as an open rate.


Has anyone experienced something like this? Did you develop any solutions for emails going forward? Could this be a spam filter issue? I ran our emails through a free spam tester online but received fine results.