I checked the header data for a suspicious email that claimed to be a newsletter purportedly sent from Microsoft. The actual sender domain was @phx.gbl. A couple of WHOIS searches failed to find such a domain (not even just ".gbl"). I did notice in the results of a Google search that many newslist posts have this domain, but could find no specific discussion of its meaning. Should I be concerned when I find this domain in the sender address? I have not opened the main body of the message.
I don't submit many questions because I am not clear on the rules or expectations. This seems like a question a network expert would know the answer to, so I have rated it as easy. If I am wrong about this, please give feedback and I'll be more generous in the future. Thanks.