Route53 - Hosted Zones - MX record

When a change is made to an MX record in an Amazon Route 53 hosted zone, this activity is logged through AWS CloudTrail. CloudTrail captures API calls for Route 53, including changes to DNS records such as MX records. This provides an audit trail of actions taken by users, roles, or AWS services within your Route 53 configuration.

Additionally, you can enable DNS query logging for your Route 53 public hosted zones. When enabled, Route 53 will publish logs to Amazon CloudWatch Logs that include information about DNS queries made to your hosted zone. These logs contain details such as the domain queried, date and time of the query, DNS record type (like MX), and DNS response codes. This feature helps address security and compliance requirements by providing visibility into DNS activity.

To get comprehensive monitoring, you should ensure both CloudTrail is enabled for API activity logging and DNS query logging is configured for your Route 53 hosted zones.
Sources
Security Hub controls for Route 53 - AWS Security Hub
Does AWS do internal logging for user access information for AWS services? | AWS re:Post