[dns-operations] Can MX be working with CNAME?

[Doug]

Hello,

$ idig plus.google.com mx
plus.google.com.    1200    IN    CNAME    plus-china.l.google.com.
plus-china.l.google.com. 600    IN    MX    40 alt3.aspmx.l.google.com.
plus-china.l.google.com. 600    IN    MX    50 alt4.aspmx.l.google.com.
plus-china.l.google.com. 600    IN    MX    10 aspmx.l.google.com.
plus-china.l.google.com. 600    IN    MX    20 alt1.aspmx.l.google.com.
plus-china.l.google.com. 600    IN    MX    30 alt2.aspmx.l.google.com.

I never saw this type of MX.  Are they valid records?

Thanks.