mailchimpapp.net has no MX records.
Question and response
Question
dig mailchimpapp.net. MX
Answer
The response has no answer records.
Authority
mailchimpapp.net. 600 SOA a1-205.akam.net. domains.mailchimp.com. 2014031627 10800 3600 1209600 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0