You can use MailSlurp's REST API to query domains to determine a servers IP address. Here is an example using curl.
curl -X POST "https://api.mailslurp.com/mail-server/describe/ip-address?name=www.mailslurp.com" -H "accept: application/json" -H "x-api-key: YOUR_API_KEY"
x-api-key header: this is your free API Key. Sign up to create an account.