My IP address workaround was just a make do thing, not a fix, it either works or doesn't dependant on the IP and whether Google got to it yet or not, it is not a fix and should not be considered as one.
aspmx.l.google.com can only be used to send to a gmail account or another google apps user account (Anything hosted by gmail), it has to be able to work as it uses no encryption of any kind on port 25. If it won't work you need to go into the gmail account and enable less secure apps.