mail1.aweber.com has no CNAME records.
Question and response
Question
dig mail1.aweber.com. NS
Answer
The response has no answer records.
Authority
aweber.com. 1800 SOA josh.ns.cloudflare.com. dns.cloudflare.com. 2396325906 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0