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SBS 2008 POP3 connector problems with maximum message size

Last Modified: 2012-05-06
I am having problems getting the system to download larger emails (20 mb and over - but this is variable).  Initially the log complained that messages were over the maximum default 10 mb size.  I altered the settings in Exchange Management Console:
Organisation, Hub Transport, Global Settings, Transport Settings - max send/receive set to 50720
Organisation, Hub Transport, Send Connectors, Windows SBS Internet Send - max. message size box unticked
Server, Hub Transport, Receive Connectors - all 3 receive connectors set max. message size to 17480 - too small I know - but it was set larger and I got the error below.

This did in fact allow the connector to download emails up to the 17480 limit.  BUT if I set these limits up higher (say 50720), the POP3 connector would fail to download the large emails (15-20mb - so well below this limit) with this error:
Cannot connect to the SMTP server 'localhost' on port 25. The error code was 0x800ccc0f. Verify that the Exchange Transport service is running and that the Exchange Receive connectors are properly configured.
This error would only occur if there was a large email in the POP3 box - if there were no large emails then there would not be any errors.
By dropping the Receive connector sizes down to marginally above the size of the email to be collected - it would eventually collect it.  By the way, I can Telnet to Localhost on Port 25 no problem.
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Top Expert 2013

The practical limit for e-mails is 5-6MB. Anything larger even if the server is set to the default of 10MB or greater can result in failures due to the servers that handle the e-mail during transit. For larger files you are better to set up an FTP server, VPN, or make use of Sharepoint services, built into SBS.


Problem is that this is an upgrade from SBS 2003, where there were no problems with collection of POP3 mail.  So it makes it difficult to not to draw the conclusion that this is not a problem with SBS 2008 (or at least its configuration).  I also don't think the end user will accept that these emails ARE handled by the ISP POP3 box, but will not be handled by his own server.
I can work around the problem by setting up POP3 collection directly from the Outlook client, which will download the email without complaint - but this is not what we want of course.
Top Expert 2013

20MB is just not a reasonable size for e-mail.
However, have you seen the following post. Found a link to it in a message board saying it resolved a similar issue. They are saying the FAX message size limit also affects e-mail. You might want to have a look at it:


Robwill thank you for the information. I had discoverd by trial and error that the Fax Sharepoint receive connector need to have its limit increased in order to receive larger emails, along with the Default and Internet Receive connectors.
Now all I need to do is find out why larger emails provoke the error:
'Cannot connect to the SMTP server 'localhost' on port 25' etc. as detailed in my original post.
I suspect it is something to do with the Fax Sharepoint Receive connector again, as this is the only one that is set to connect to (localhost) on Port 25.
Top Expert 2013

Sorry I have no further ideas on the error. The main issue is the fact that messages of that size are just not practical as they could conceivably be received when sent/receive through one path, and blocked through another when a different mail relay is present.
Due to this reason, most institutions such as universities 'post' notices that their systems can forward an e-mail up to a maximum of 20MB, but recommend 10MB be the limit used by clients, and that it is possible that anything over 5MB may not reach the recipient. Assuming you can configure Exchange appropriately, this could still cause other issues between sender and recipients. It is not a good practice to support, though I understand if users have succeded in the past it is hard to change them.


I think I am getting near the crux of the problem now.  The Exchange connector system is timing out after 5 minutes, which is not enough time to download the larger email.  This is the relevant excerpt from the POP3 Connector Log:
[t 0] 05/11/09, 17:14:11: Downloading message 1 of 11.
[t 0] 05/11/09, 17:14:11: (POP3) [TX] RETR 1
[t 0] 05/11/09, 17:14:11: (POP3) [RX] +OK Message follows
[t 0] 05/11/09, 17:19:12: (SMTP) [RX] 451 4.7.0 Timeout waiting for client input
[t 0] 05/11/09, 17:19:12: (AsyncConn[ localhost:25 ]) Connection to 'localhost' closed.
[t 0] 05/11/09, 17:19:12: (SMTP) ERROR: "Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity.", hr=800ccc0f
[t 0] 05/11/09, 17:19:12: Failure hrResult (0x800ccc0f) trying to connect to SMTP server 'localhost':
[t 0] 05/11/09, 17:19:12: (no response)
[t 0] 05/11/09, 17:19:12: EVENT: Cannot connect to the SMTP server 'localhost' on port 25. The error code was 0x800ccc0f. Verify that the Microsoft Exchange Transport service is running and that the Exchange receive connectors are properly configured.
[t 0] 05/11/09, 17:19:42: (POP3) [TX] QUIT
[t 0] 05/11/09, 17:19:42: ERROR: 0x800ccc05 ("IXP_E_NOT_CONNECTED") at d:\wssg_src\sbs_cougar_rtm\sbs\src\messaging\pop3\ixpbase.cpp:474.
[t 0] 05/11/09, 17:19:42: (POP3) [RX] +OK
[t 0] 05/11/09, 17:19:42: (AsyncConn[ pop.iomartmail.com:110 ]) Connection to 'pop.iomartmail.com' closed.

What is AsyncConn exactly? I tried altering the ConnectionInactvityTimeout parameter on the "Default <ServerName>" Receive Connector - but it is still timing out after 5 minutes - so it must be somewhere else.
Top Expert 2013

The exchange pop connector has a default minimum of 15 minutes, though this can be hacked in the registry to be shorter. In companies with many employees, i.e. large quantities of e-mail, this has to be lengthened. If downloading very large e-mails the same would have to be adjusted. Clients of course do not like this as it means there e-mail is updated less often. This option is located under: Server management | manage pop3 e-mail | open pops connection manager | scheduling

You can get around this by using direct SMTP reception of e-mail rather than using the pop connector. Though the pop connector will work forever, it is intended as a short term migration solution to using SMTP.


15 minutes is the default minimum schedule time (or at least it was with SBS 2003 - in SBS 2008 you seem to be able to set it shorter if you wish).  However this timeout is occurring after 5 mins of starting the POP3 collection process, so it is something completely 'other' than the schedule timing.  I will post this specific query as a separate thread - see if anyone has come across it.

There are very specific reasons for not wanting to use SMTP mail delivery (which I have done with some of my other clients if they want it).  The most important one being that users can continue to collect their email from their POP3 boxes in the event of failure of the SMTP server, or of the internet connection (they can connect to the internet elsewhere and collect their mail).  The root cause of this problem, I believe, is not POP3 email or large emails.  It is the configuration of Exchange 2007 within SBS 2008.  Don't forget that it worked absolutely fine in SBS 2003.  I am a little baffled as to why Microsoft seem to have a problem with users who prefer to collect their email via POP3?

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I have the following problem, I have a UTM from SBS 2008 POP3 connector, but all emails with more than 2MB, trapped in the web mail and not delivered to the mail box in exchange.
the error it gives is:

The TCP / IP connection to the server smtp.server was completed when trying to access mailbox 'mailbox'. The causes can be server problems, network problems, a prolonged period of inactivity, a time limit of the connection or incorrect connection settings.

how can I solve this problem.
Top Expert 2013

Hi ajgveiga.
This is an old closed question, you will need to start a new question of your own, which will also attract more folk to assist.

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