Most of the audience emails is on Gmail, so it is necessary to track domain sending reputation on Google Postmaster service. Available from google administrator panel
If reputation of IP domain drops below average, action required
General reputation monitoring and spam testing
Service that I usually use to check domain reputation: mxtoolbox
To Check domain reputation you need to go to blacklists tab and enter a domain address or IP address
If IP address or domain is in more than 2 black lists, you have to take action on it