_mailcust.gandi.net has no MX records.
Question and response
Question
dig _mailcust.gandi.net. MX
Answer
The response has no answer records.
Authority
gandi.net. 1200 SOA dns0.gandi.net. hostmaster.gandi.net. 2026021801 900 900 1209600 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0