Here is a really strange problem we are having between our 2 companies, which no one so far seems to be able to figure out.
Our company is in the Seattle area and is connected to our parent company in Russia by a VPN. The VPN, firewall, gateway solution for both our offices is IPCop (1.4.1 in Seattle, 1.3.0 in Russia).
In the Seattle office we have postfix server using Courier-IMAP with a POP3 daemon on a Linux server.
Last Friday, when the Russian personnel came to work, they were receiving their mail just fine for about 2 hours. Then 5 employees (and only 5 specific employees) were no longer able to receive any mail. They were all using POP3.
In the logs I could see that they would LOGIN and the there would be an immediate DISCONNECTED. Given the error they were getting at their end, it was as if they would connect and login to the server, but certain networking issues caused the server to believe that it had lost connectivity with those users.
The IT Admin on the Russian side was one of the 5 experiencing problems. His computer was set up to pull mail through a mail proxy server in their office. So, I told him not to use the proxy and circumvent it. Just go directly to our mail server through the VPN. He started pulling mail fine.
AHA! The culprit was the mail proxy server. Wrong....
It turns out only a few people were going through the proxy server. The IT Admin in the Russian office went to the remaining 4 employees having problems and switched them to either using the proxy or not. In the end only one other of the employees starting pulling mail. In his case, he went from going directly through the VPN to going through the mail proxy in order to pull mail. Very strange. I had him try reconfiguring the remaining three to go through the Internet (not through the VPN), but that didn't resolve the problem either.
I asked him if they had any switches over there. Turns out they had several.
Since he didn't want to shut down the switches till the office was empty, we tried one other solution.
We switched the remaining 3 from POP3 to IMAP. It worked! But why?
That evening when the office emptied out, he shut down all the switches for 10 minutes. As I understand 2 of the 3 remaining employees nonetheless cannot get mail through POP3, but IMAP works.
So, I was wondering why this might be the case? What could possibly be going on? What tests could we do to see what's going on?
BTW, we did do telnet sessions from the client computers. What happens is the clients LOGIN through POP3, but then a disconnect happens.
Curtis Vaughan
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