The simplest approach is ..
.. to check out where their email goes.
[00] moi@machine:~
$ dig +short mx anchorfree.com
1 aspmx.l.google.com.
10 alt3.aspmx.l.google.com.
5 alt1.aspmx.l.google.com.
5 alt2.aspmx.l.google.com.
Why am I not surprised? Next!