Email service providers treat domains differently based on their reputation. This “score” can be based on many things, such as the age of the domain name, how well the sending account has been set up, deliverability, engagement data from users receiving email from it, and – often to a higher degree – previous listings of domain names and IP addresses on anti-spam services such as SpamHaus.
You can use MXToolbox to check your domain and IP reputation against many popular blocklists.
