mta1.artelecom.pt has no CNAME records.
Question and response
Question
dig mta1.artelecom.pt. NS
Answer
The response has no answer records.
Authority
artelecom.pt. 10800 SOA dnsh01.artelecom.pt. suporte.artelecom.pt. 2026030401 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0