Hey yiggory,
You may want to utilize an external service for email delivery like Sendgrid to ensure that your emails aren’t getting delivered to junk/spam folder.
The setup would involve setting up DKIM in domain name records and is little complex but you should be able to get support for that in Sendgrid’s forums.
Although, even this won’t guarantee the solution you are seeking for because email’s delivery depends on following factors too:
1. Service provider’s filters approve the email or not.
2. Users’ personal filtering & spam reporting habits.
Regards,
Mayank