tailscale2.slc.efscloud.net has no MX records.
Question and response
Question
dig tailscale2.slc.efscloud.net. MX
Answer
The response has no answer records.
Authority
efscloud.net. 900 SOA ns1.efscloud.net. efscloud.net.domainsbyproxy.com. 393 600 300 3600000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0