Send a double opt in or a welcome email: This will help users to get verified. If the first of many emails goes straight to the spam folder, there are a couple of things you can try to do. First, contact your contacts to ensure that the email does not go to the spam folder by marking them as "not spam". This will tell the ISP that the email should go to the main inbox going forward. The alternative to that is to request your audience to add you to the safe email list
Get a verified domain: This may sound simple but if you buy your email domain and you own it will be easier for email marketing. It's essential if you own the domain and will improve your likelihood of not ending up in the spam folder