Hi @Abimbola ,

Welcome to the Community.

The answer can be a bit complicated but at the highest level, it all comes down to your email content and how relevant it is to your subscribers, and who you are sending your emails to on a regular basis.

Subscribers can mark an email as spam for any number of reasons but the most likely scenario is that they simply no longer want to receive your emails and instead of unsubscribing within the email, they simply click the Spam button in the email inbox. 

Why someone no longer wants to receive your emails usually is a condition of the content. If users no longer feel the emails meet their needs or are relevant to them, they will likely unsubscribe or mark the message as SPAM.

Unfortunately, as more subscribers mark content from you as SPAM, the ISPs (Gmail, Yahoo, Hotmail, etc.) take notice and based on user behavior they start to filter the messages as junk because they see more and more users marking the content as spam. 

The other side of this equation is who you are sending your content to. On a regular basis you want to send your messages to your most engaged contacts - people who are most likely to open and most likely to click. So, you segmentation strategy will play a big role here. If you are sending to your most engaged subscribers and they continue to open and click your content, then the ISPs will continue to deliver your emails to the inbox. 

But overtime, if you see your open and click rates decrease and more subscribers unsubscribe or mark the content as spam, its an early indicator for you to test new content for your subscribers. 

This combination will help you ensure you don’t end up in the Junk folder and will help you keep spam complaints and unsubscribes low.

Unfortunately there is not one specific tactic that will keep you from receiving Spam complaints, but more of a longer-term strategy and mindset to use within your email program.

Additionally, here is a related post.