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Exchange randomly rejecting IMAP authentication

Posted on 2008-10-20
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Last Modified: 2013-11-29
Our exchange server has developed an issue in recent weeks where it will randomly kick back a prompt that the entered password is incorrect. This is happening both with computers on the local network, and remote access. No configuration changes have been made to the server, and the server is functioning as most of the time just re-entering the password allows it to authenticate and retrieve mail.

I am wondering if there is some kind of time-out setting in Exchange that might be returning an incorect password message too quickly. I have been monitoring the server and the system load, both CPU and network wise, is pretty minimal. The password request comes up at random intervals, sometimes 15 minutes apart, sometimes a couple hours. Nothing obvious is jumping out at me as to what might be the cause.
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Question by:ArthroWaveIT
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by:moorhouselondon
ID: 22761957
There is a Time Out setting for IMAP in Outlook which it looks like might need lengthening.  This is in the Advanced settings.
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by:ArthroWaveIT
ID: 22769470
I have tried adjusting the time out setting in outlook, and it does seem to make the authentication rejected popups less frequent, however this does not really solve the issue. Something in Exchange is not responding properly. I am wondering what might be causing the rejection itself from Exchange, since the password is correct and the account is active. The email clients are checking mail every 5 mintues or so, and most of the time it works fine. The server is not over used and the network bandwith being used by the server is generally quite low. This is happening on the local network, so network latency seems unlikey.
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by:moorhouselondon
ID: 22769554
You don't have accounts where there are thousands of emails in the IMAP folders?  If these headers are pulled down from the server regularly enough the Client could be processing the last request when a fresh request is issued.
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by:ArthroWaveIT
ID: 22769764
While some of our accounts do have a lot of messages in them, this issue still occurs on accounts with less than 100 messages in their mailbox, and a relatively small mailbox size. Also, the issue just started happening a couple weeks ago, and the larger mailboxes have been large for quite some time before that, with nothing in the configuration or setup being changed. Your comment makes sense as a possibilty, but I am still missing something that has caused this issue to manifest recently.
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moorhouselondon earned 150 total points
ID: 22770348
Is this happening to particular users on a random basis, or is it always the same users?

Time to get Wireshark involved maybe?  First of all just filter IMAP traffic into and out of the server - do you have a Switch that has a port that can be used as a monitor?  Start Wireshark capturing, then halt it when anyone gets a password prompt.  There will be a lot of traffic but it can be further filtered to test various hypotheses.
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