I have now discovered that the problem must have something to do with our SMTP server. It turns out that our users were not having trouble receiving messages over the POP server, they just thought they were. The real problem with them also was with the SMTP server.
I also tried sending a test message using Thunderbird, and it came back with the same problem that Outlook had.
In our office, everyone's Outlook started acting screwy this morning. Three of the people in our office are unable to receive email through Outlook, and two of us are unable to send. Everything was working fine yesterday, but today it's all messed up. Every time we try to send or receive (depending on who's trying to do it), we are prompted for our password, and no matter what we type into the prompt, the password prompt pops right back up again.
We are able to access the server through our web mail, but we are not able to access it through Outlook.
Anyone know if there's something going around that might cause this? Did one of our Microsoft updates possibly break our Outlook functionality? We are all using Windows XP SP2 (we've been on SP2 for a while now, so it's not that), and some of us are using Outlook 2000 and others are using Outlook 2003.
Any thoughts? I've contacted customer support for our hosting package as well, but since it seems to be a problem specific to Outlook, I'm doubting that it has to do with our host.
I should note that the other three accounts I have configured in my Outlook are working just fine (and two of those accounts are hosted by the same provider that's hosting our main account).

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