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Exchange 2007   - email client connectiion is being blocked WSAEWOULDBLOCK

Posted on 2010-09-10
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Last Modified: 2012-05-10
Hi..
I have custom email client that used to work fine connecting -  to previous versions of Exchange.
With Exch 20007 the client connection is blocked and returns a  windows socket error of WSAEWOULDBLOCK.   Outlook 2007 connects fine.  I tried using port 135 too...
How can Outlook connect and a winodow socket program can not.  Any ideas?
thanks
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Question by:JElster
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by:michael_b_smith
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well, the first question has to be: what technology is the program using?

MAPI requires "all ports".

WebDav requires TCP 80 or 443.

EWS requires TCP 443.
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by:JElster
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It's written in C# using Microsoft .Net    System.Net.Mail.....  you specify the SMTP server and port and user / passs
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by:ar_m
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Outlook could sent mail without use SMTP protocol. To send emails by SMTP you need that Exchange Server have the SMTP port listening. Check it : telnet <Ip server> 25 / telnet <Ip server> 465 (SMTPs)
If it not close the socket:
EMC: Server Configuration: Hub Transport, select your server and create a Receive Connectors
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by:Dave
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Possibly The windows firewall knows about Outlkook and  you need to add and exception for your program. Could be other firewalls or anti virus.
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by:JElster
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Telnet did not work... just hung..
The workstation has the firewall off.
How can the Exchange server know that the 'request' is coming from Outlook and block everything else...is that a firewall issue?
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by:Dave
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If you are using Outlook using MAPI thats a different protocol to SMTP and port 25 and uses different ports. SO exchange can tell by the ports you use. SO Exchange can be configured

if you hjave McAfee installed that will block access to Port 25. What other protection software is installed on the PC? Norton, McAfee?
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by:JElster
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I uninstalled Trend Micro.. so no virus scan software in on it.    The setting in Outlook just have the name of the Exch Server.
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by:Dave
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not sure whats going on. Can you post a snapshot of the dialog that has the exchange server name..
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by:Dave
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sorry I meant the outlook dialog box with the exchange server name in...
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by:JElster
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It's just the standard Outlook setting screen when connecting to exchange.. with  a text box for Microsoft Exchange Server
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by:JElster
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Looks like the windows network user/pass is 'tied' to the Exchange Server....
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Dave earned 500 total points
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According to MSDN "The System.Net.Mail namespace contains classes used to send electronic mail to a Simple Mail Transfer Protocol (SMTP) server for delivery" So it needs to connect on port 25.

OUTLOOK does not use SMTP to submit messgaes when its configured a an Exchnage client so it doesn;t need to connect on port 25. It uses MAPI and usually connects on a random port negotiated by the port mapper service.

So its entirley possible for Outlook to work and the system.net.mail namespace to fail.
Even worse, on Exchange 2007 (and 2010) the client access roll which handles MAPI connection may be on a different server to the Hub/Transport roll that handles SMTP message submission. On Exchange 2010 there are recomendations that mail submission uses a different port (465) and SSL.

I suggest you have a chat to your Exchange admins...
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