My G Suite gmail personal emails to people are sent to spam

I was one of the pioneers of the free Google G Suite (formerly Google Apps) package. So I created a small custom domain and email for my family. It is limited to 50 users, but it is much more than what I need or use.

In the last few weeks, many e-mails that I sent by myself (for example, no replies) have been sent to my recipient's junk mail folders. Ironically, even a family member who has the same domain name as the one I am on! All the people involved are on Gmail, but these are just people I know.

I have no problem receiving emails from other people.

I am not a marketing specialist and I use e-mail only for personal purposes – nothing automated has access to my account. I have never had this problem until just recently.

What can I do?