front.mail.ziggo.com has no CNAME records.
Question and response
Question
dig front.mail.ziggo.com. NS
Answer
The response has no answer records.
Authority
mail.ziggo.com. 59 SOA ns1.flowmailer.net. contact.flowmailer.net. 2026021602 86400 7200 7200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0