DNS Search Domains are the reason: they're a mechanism for resolving a hostname to a fully-qualified name. Many companies I've worked for would (for example) h

DNS Search Domains are the reason: they're a mechanism for resolving a hostname to a fully-qualified name. Many companies I've worked for would (for example) have a search domain set for 'wherever.internal', so if you typed 'jira' then having failed to find the 'jira.' TLD, the local DNS resolver would then try to find 'jira.wherever.internal'. That way, you could correctly resolve hosts based on just their names and avoid extra typing. The problem comes when machines move off the corporate network but keep their search domains. Now we're making public lookups, and the network infrastructure has no idea how to resolve the names you're looking for. In an AD environment, the AD server is typically the DNS server and does know how to resolve the AD domain as a name. So the machine's lookup for 'corp' works. But move off the AD network and we're back to search domains. And apparently enough Windows machines have a '.com' in their search domains for there to be a lot of 'corp.com' lookups. Which cause the problems listed when they succeed. If you put '.net' in your search domains then corp.net would have the same issue. What I'm still not sure about is that I'd thought that you needed an _explicit_ search domain. Maybe there's enough AD servers set up to hand out '.com' as a literal search domain?