Engagement plays a huge role in email deliverability.The average number of legitimate business emails received each day has remained static since 2015 , but the number of Spam emails that bypass security filters (spam that actually hits your inbox) has risen from 12 emails per day in 2015 to 16 emails per day in 2017.
That means one out of every five emails sent either gets filtered as spam or blocked entirely. One of the big reasons that it is getting harder to avoid emails going to spam is that spam filtering has become more rigorous. Web mail providers are simply cracking down harder on spam. However, the filters aren’t 100% accurate, so sometimes legitimate emails go to spam too.