I can ping the Exchange server here at work, but Outlook doesn't connect to it. I've verified the server is indeed the Exchange server and I've tried using the IP instead of the server name. I am also able to connect to port 135 using telnet (although nothing useful happens). I also tried running a trace using Wireshark but the protocols Outlook uses are proprietary and I couldn't see anything useful in the trace.

I'd love to hear some other steps I could take to track down the problem.

  • Are all of the services running? What does the eventlog say? Is the Windows Firewall service blocking ports? Jun 8, 2009 at 8:22
  • Are client and server in the same subnet/LAN?
    – splattne
    Jun 8, 2009 at 9:47
  • My first question is which version of Exchange are you running? If you're running Exchange 2007 or 2010, are all of the roles running on the same server? Which version of Outlook are you trying to connect with?
    – smassey
    Aug 24, 2011 at 4:25

9 Answers 9


In our case the problem was with one of the routers along the way whose MTU was set to a low value. The packets sent by the RPC protocol were getting split and that for some reason prevented Outlook from working properly.

To determine the largest packet size that can get to the server, use the following command:

C:\> ping myserver.com -f -l 1500

Replace 1500 with different values to determine the maximum size of the packet. After you know the value, use the instructions here to set the MTU size for your network connection.


Use RPCPing - http://support.microsoft.com/kb/831051

Is this just one client that can't connect? Is it all of them? Does OWA work? (No point even trying to get outlook to connect if the server itself can't connect to mailboxes).

Are you sure you've installed all the correct roles on the exchange server? Is there a firewall or Antivirus software in the way somewhere (including on the server itself) blocking traffic?


The rectifications from microsoft didn't work for me. In the end created a new user profile for logon to windows. This fixed the Outlook 2010 connect to exchange server problem and also problem of having to keep supplying passwords to imap accounts. Presumeably my previous user profile was corrupted in some way.


It looks like you are trying to connect with the mapi protocol, maybe you can try to connect with imap or pop in first place to see if it works you can telnet to port 110 to see if pop3 is responding, you can also check on the exchange server if all exchange services are started.

if you're connecting via HTTPS (outlook anywhere), maybe the certification authority is not trusted.

Maybe there are there is some Antivirus issue on the client machine, if happened to me with xxx Endpoint.

Check that the machine name is correctly resolved by netBios ans DNS.

Hope this helps.


When you setup a profile in outlook you select exchange server for type, when you specify the username/server name does this name resolve properly? Blank them out first if they have been resolved before and try again.

Do any other workstations work?

Hate to say this.....reboot exchange?
If the the name does not resolve reboot your domain controllers, then the exchange


There are several possibilities I can think of immediately, but you should have included the exact error message you got when Outlook couldn't connect, which will help everyone here to narrow it down.


I agree with Robert, first verify that you can connect to the exchange server via an alternate protocol, either OWA or POP3/IMAP.

I would also recommend inspecting the Event Viewer on your exchange server. One of the issues that I come across regularly is that of the user being disconnected from Exchange because they have exceeded the MAPI session limit (defaults to 32). Why this happens I don't know yet, but a restart of the Microsoft Exchange Information Store service (and the associated Auto Accept Agent) does the trick for me.

I think this comes down to "mobile" users moving being wired and wireless connections to our network


What OS are you running. If you are running XP, I know this sounds simple, but the first think i would do is run updates. If you are using outlook as your mail client, i would also install Office SP2.


What worked for me was a combination of regedit: HKCU\Software\Microsoft\WindowsNT\CurrentVersion\Windows Messaging Subsystem\Profiles and delete the existing profiles

and uninstall the most recent office patches. After this was done and email account established, I reinstalled the updates. Everything is working.

The OS is XP Pro sp3; Office 2007

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .