There are several records that are used to setup and secure your email services.
A mail exchange record (MX record) is a resource record or settings within the Domain Name System (DNS) that redirects email to a specified mail server that accepts email on behalf of a domain or users. Within an MX record you can set routing priorities using preference values for which mail server will be used if there are multiple servers.
www.techopedia.com/definition/1685/mail-exchange-record
Sender Policy Framework (SPF) records allow domain owners to publish a list of IP addresses or subnets that are authorized to send email on their behalf.
mxtoolbox.com/spf.aspx
Domain-based Message Authentication, reporting and Conformance record controls what happens if a message fails authentication. It tells a server to either Quarantine or reject the message or allow the message to be delivered. It also sends a report to an email address/es with data about all messages seen from the domain.
Editing these records and keeping them up to date allows Atcom Host to prevent your domain from being used for spam and spam being sent to your domain. These records also add to your online reputation. These records also work with your unique domain key as well.