I tried to send e-mail from the system to realize fax transmission. However, I attempted to send to eFax’s e-mail address (domain part efaxsend.com), but in the qmail mail log

Deferral: CNAME_lookup_failed_temporarily. _ (# 4.4.3)

It is recorded as a differer and can not be sent.

As a cause,

I can not resolve the destination […]