You have
zzzz@ddd.org and zzzz@ddd.orgg and
zzzz@gmail.com - three distinct addresses. I sometimes wonder why people think of obfuscation of domain names when they have problems.
You feel that we should work out the MX records for
ddd.org and ddd.orgg and figure out that your unnamed Linux mail server is the destination MX??
Well, just check your
main.cf (I think) and see if your server is listing whichever domain as 'local'. This is a very basic configuration.
# The mydomain parameter specifies the local internet domain name.
# The default is to use $myhostname minus the first component.
# $mydomain is used as a default value for many other configuration
# parameters.
#
#mydomain = domain.tld
I see the default postfix/
main.cf is well commented to help you out:)