CNAME & MX record confusion.

[John Wobus]

If you make a DNS name into an alias for another DNS name
using a CNAME record, e.g.,

myalias.example.com. CNAME www.example.com.

then all the MXs for www.example.com also apply
to its alias, 'myalias.example.com'.  Same for any other
DNS records for 'www.example.com'.  Any record
for www.example.com also applies to 'myalias.example.com'.

As simple as this concept appears as stated above, it's
implications often confuse people.  For example, it does not matter
that your purpose for setting up the CNAME was strictly
for the benefit of web serving.

Furthermore, you cannot have other DNS records for an alias
such as myalias.example.com.  To do so would be like saying it's
an alias and it also isn't.  An alias is an alias and can be nothing 
else.

When someone, who is used to setting up 'name virtual'
webservers using CNAMEs runs into problems with these restrictions, 
typically
they switch to using A records instead of a CNAME.  If www.example.com
has one A record with number 192.168.1.99, then you also
deploy this record:

myalias.example.com. A 192.168.1.99

Then you can give that name its own MX record(s).

John Wobus