Regarding this line:
Mar 19 22:57:26 g4x sendmail: gethostbyaddr(192.168.100.10) failed: 3
Use NetInfo. Under the "machines" property, duplicate "localhost," give the new entry a name (that is, name your machine -- "imac" or whatever), and change "ip_address" to the IP address assigned by your router.
Note, if your machine obtains a dynamic IP from your router, this will fail when the IP changes. I've configured my router to never change the IP address for the machines on its network, once assigned.