EXN0V4 wrote: As a general rule of thumb, pulling down a new IP address and flushing your cache at least once a week is a good idea anyway.
Well it's not a bad idea, but no it is not a good idea either. Release + Renew will almost always give you the same IP, and what IP address you're on makes absolutely no difference anyway. It's sort of like the house number on your street, whether you're 55 or 57 it only matters that the mail is getting to you.
Flushing the cache is fine but that's not what flushdns does, ipconfig /flushdns just flushes out the DNS records you've got stored and forces the computer to look them up again, a process which happens frequently.
Neither of these will touch the cache of any of your browsers and so won't solve the problem, just Ctrl+F5 and you're good to go. I wouldn't even bother clearing the whole cache if you can avoid it, just Ctrl+F5 on any websites you get problems with.