192.168.X.X are internal IP address of any LAN (Local Area Network) - anyone can use this setting in their internal LAN - if you are getting emails from (hisname)@192.168.X.X that may be you local machine sending those email. You may have a virus that is creating this email. To check your IP address click start and click where it reads run - type cdm and a black windows will pop. Then type the command ipconfig and hit enter and you will see the local IP address of your machine.
I used to have the same problem on one of my PCs. There was a trojan/worm that was sending a huge amount of emails out there. I didn't knew what to do because the antivirus I had, could detect the problem but cannot fix it. Even more, there was some strange ip address logs on my pc. On a simple netstat, I saw some IPs listening on weird ports like : 65155, or something like that. I checked those ip addresses on this
ip lookup tool, and I discovered that some IPs were from countries I didn't have any conecctions with. Finally but sadly, the latest resort for me, was to erase the full HDD partition.
You might wanna check you conputer online. Check it with bitdefender or something.
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the benefit to this would (I am assuming) phone based tech support. 
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