I had this problem on my site site as well. I was originally using the local mail option to send emails. However, using local mail will get your emails sent to the spam folder. Once I switched to a smtp option the emails were no longer considered spam. I also changed my outgoing email from noreply@domain.com to system@domain.com. I have found when using a noreply@domain.com emails will most likely end up in the spam folder.
After changing how you are sending the emails and you're still getting the emails going to the spam folder, another tip is to change the message content. Email service providers will automatically send emails to the spam folder that have similar content as previous emails that were marked as spam.
This worked for me and should work for you.
