Emails going to spam / promotions folder

A lot of emails that I am trying to send via infusion soft is ending up in spam/ promotions folder. This is happening in email broadcasts as well as single individual mail. I have tried this on a test email where I have sent more than 10 emails as well as on some real client emails. How do I ensure that this does not happen?

Can anyone guide me on this. Any help would me much appreciated?