Regarding my last question. I know now, that problem lies in slow DNS resolution. What can cause that, if user says that he has problems only with that one particular domain.
Slow resolution:
example.com
foo.example.com
allsubdomains.example.com
Weird thing is that user has no problem with another domain on same DNS server, redirecting to same IP as example.com
.
And btw. shouldn't be domain somehow cached on user end? Because he has all the time problem with slow loading. I told him do flush DNS cache in Windows, but that doesn't helped.
Unfortunately I can't debug DNS server, because we are using our domain registrar DNS servers.