mta1b1.update.trulia.com has no MX records.
Question and response
Question
dig mta1b1.update.trulia.com. MX
Answer
The response has no answer records.
Authority
trulia.com. 900 SOA ns-1430.awsdns-50.org. hostmaster.trulia.com. 1 7200 900 1209600 30
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0