It can be very frustrating for end users when they repeatedly try to send or receive email only get the same error over and over again. And if it’s an error message related to problems with a connection then users will have a tendency to continue trying that connection until they reach their frustration limit and wind up in front of their administrator’s desk.

This can happen if you’re running Outlook and trying to send and receive email to a server such as Exchange Server using the Post Office Protocol (POP3) or the Internet Message Access protocol (IMAP) then the following error message may be produced:

“Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Account: ‘account name’, Server:’server’, Protocol: POP3, Port 110, Secure (SSL); No, Error Number: 0×800CCC0F”

There are various reasons for this error message to happen some of which include: server problems, network problems or long periods of inactivity. Anti-virus or firewall software application can also cause this error message to occur due to interference. If you suspect it is your anti-virus, firewall or maybe a proxy server that is causing the problems then a review of your configuration settings will be necessary.

An administrator can step through the troubleshooting process by temporarily turning off their antivirus application and then checking to see if email can be sent. If you’re able to do so then you know that the problem lies with the antivirus configuration, settings, version or an incompatibility. Likewise you can turn off your firewall software and check again if email can be sent. If not then the same potential trouble spots will need to be reviewed.

Another troubleshooting technique that an administrator can employ is to try to telnet into the ports on the server that are associated with email. An administrator can try telnet or PuTTY to open a connection on the server using either port 110 (POP3) or 143 (IMAP). Normally a connection will be made and communication can occur. But in this case when the POP3 or IMAP banner appears, the connection is dropped. An error message then appears which says: “Connection to Host Lost”.

This is an indication that “bandwidth throttling” has been turned “on” by the Exchange Server administrator in Exchange 2000 Server or in Exchange Server 2003 which is the most likely cause of the error messages.

Bandwidth throttling can be used to block read requests, but allow write and transmission requests to still occur. Blocking read requests first are the most likely target as read requests can produce further requests to occur. It can be a useful tool for keeping the bandwidth within preset limits. Managers of data centers or other computing service providers can use this tool to help them meet various service level agreements by ensuring that resources and bandwidth is always available.

There is a set of counters that are activated by Internet Information Services (IIS) when bandwidth throttling is enabled. These counters show up in System Monitor (SysMon) and are labeled at “Async I/O”. When bandwidth throttling is enabled the counters will report the corresponding counts. When bandwidth throttling is not enabled then the reported values will be equal to zero.

These counters can be useful to count how many requests are being blocked and rejected. The counts are displayed as cumulative totals which can be helpful to chart usage over time.

You should note that having “bandwidth throttling” turned on or off does not affect POP3 or IMAP performance. The Enable Bandwidth Throttling option can be toggled from the Performance tab associated with each Web site on the system running the Exchange Server.

Someone will need to contact the Exchange Server administrator to check whether or not bandwidth throttling has been turned “on”. If “on”, then a request will have to be made to get the bandwidth throttling turned “off” by the Exchange Server administrator.

As the administrator you need to go to the lower left corner and click on the Start button and then pull right on Programs, then bring up the Administrative Tools menu and click on Internet Services (IIS) Manager. Next, right click on Web sites and then again on Properties. Select the Performance tab and look for the Limit total network bandwidth available for all Web sites on this server option. Clear this option. Next click OK or just hit enter.