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POP3 connector won't download email for ONE account

Okay, this is weird. I am getting the following error when I check my event application logs:

An error occurred during a POP3 transaction to server <mail.server.com [username]>. The error is 1232 (The network location cannot be reached. For information about network troubleshooting, see Windows Help.
).

I have about 15 other entries in the pop3 connector and they all download/deliver their mail fine. Yes, I've double checked all the details for this account. I even entered the details straight into Outlook alongside the exchange account for this user and the mail downloaded fine (so the details are definitely correct). I've changed the password on the pop3 account. I've tried changing which exchange mailbox the mail is delivered to just for the hell of it. Nothing works. Same error as above.

From some googling I find that this used to happen if a NULL character was found in an email address or if an end of message signal was never reached...but these errors were all fixed in a service pack for SBS2000. I'm using SBS2003 fully updated (including Exchange 2003 SP2). Also apparently some characters in passwords throw off the pop3 connector...changed the password to just regular text (a smiple word) and still the above error.
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Jeffrey Kane - TechSoEasy
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tvacc

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Supposedly the pop3 connector uses multiple threads while downloading the mail...it seems that my host may be blocking it by the time it gets to the last mailbox. Is there anyway to cut down on the multithreading?
No, the Exchange POP3 Connector does not multi-thread the downloads.  MapiLAB's Native POP3 Connector does do that, but SBS's doesn't.

What make/model of router do you have in use?

Jeff
TechSoEasy
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Here's another update: I had to add another pop3 entry in the connector and now the previous troublesome entry and this one do not work. There were 17 total entries then. I then deleted two previous entries out of the pop3 connector that we no longer need and now the two troublesome entries are working without error. It's down to 15 entries and it works flawlessly. Is there some limit imposed? Any entries above 15 total just throw an error.

I was told by someone at Microsoft that it does thread them, but in any event I suppose that doesn't matter.

Right now we have a Netgear RangeMax router setup. I just had to add another user account to the pop3 connector and it is coming up with the same error.
When I had started looking at your question, I had in my mind that there was a 15 mailbox limit but when I went to confirm that, I couldn't find anything to back that up.  So... what I'm thinking is that it takes 60 seconds per mailbox and that if you have it set to poll every 15 minutes, the restart of the polling may cut it off... I'd be curious if you set the polling to longer than 15 minutes if that would allow more to get through.

But in any case if you have that many POP3 mailboxes polling, you really should convert to SMTP email, or at the very least start using a catch-all mailbox on your POP3 server instead and let Exchange parse out the messages.

Jeff
TechSoEasy
Hey there... I finally DID come across the document which talks about the 15 user level.  It's not a maximum, but there is a hotfix that repairs a problem when you are over this number.  See http://support.microsoft.com/kb/324236 for details.

Jeff
TechSoEasy
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It says that the problem was fixed with SP1 and I've installed SP1.

Anyway, is there a walk-through/tutorial on how to convert to SMTP mail (what to do on the server and with my web host)?
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Had the same problem - microsoft confirms it as a bug see below (only applies to SBS server with multiple-processor )

First, I have performed a test on my side. I have set up several POP3 connectors on a SBS server and then try to use them to retrieve emails from an Exchange Server in another domain. It indicates that POP3 connector will download messages from one mailboxes at one time. However, after further research, I found that SBS server has a default setting for simultaneous retrievals of POP3 connector. In my test, as default setting on my SBS server (single-processor machine) is set for one, it will download from one mailbox at one time.
 
In this case, the simultaneous POP3 retrieval limit which the ISP has set will impact the SBS server retrieve emails via POP3 connectors. If this limit that ISP has set is less than the SBS default setting, we may have issues in retrieving emails via POP3 connector.
 
At this point, we have following resolution/workaround to troubleshoot the issue.
 
Scenario 1
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If the SBS server is a single-processor box with no hyper-threading features, we can use the HKEY_LOCAL_MACHINE\Software\Microsoft\SmallBusinessServer\Network\Pop3 Connector\DownloadThreads registry key to control the simultaneous connections. We can configure the value of this specific registry branches to meet the ISP's requirements.
 
Scenario 2
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If you are using hyper-threaded and multiple-processor machines, the above registry does not work. This is a bug and will only be fixed in Small Business Server 2008. In this case, we need to change the POP3 Connector to use a Global Mailbox or SMTP directly to receive emails.
 
After checking the System Information in the MPS report, it indicates that your SBS server is a multiple-processor machines. At this point, we have to change the POP3 Connector to use a Global Mailbox or use SMTP directly to receive emails.