rev.vodafone.pt has no MX records.
Question and response
Question
dig rev.vodafone.pt. MX
Answer
The response has no answer records.
Authority
rev.vodafone.pt. 86400 SOA ns-a1.vodafone.pt. dnsadmin.ns.vodafone.pt. 2015091503 10800 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0