IMAP failing intermittently with one mailbox

We are in Exchange 2013 - 2010 Coexistence mode for the past two weeks, and are having some IMAP issues. One particular mailbox user is having intermittent issues with IMAP connection. About a dozen times a day, the connection fails, and the following is logged in the IMAP logs:

2014-08 05T20:19:03.041Z,0000000000036BDA,1,<2013CASIP>:993,<LOADBALANCERIP>:37619,<USERID>,61014,24,22,login,<USERID> *****,"R=""!@# NO LOGIN failed."";Msg=""User:<USER NAME>:ad73727b-7a7b-46d6-92d4-1c49d4ba3036:<DATABASE>:<2010MBXFQDN>;Proxy:<2010CASFQDN>:993:SSL;Proxy:<2010CASFQDN>:9933:SSL"";ErrMsg=ProxyTimeout:ProxyNotAuthenticated:PreAuthTimeout;Excpt=""No connection could be made because the target machine actively refused it <2010CASIP>:9933-SocketException"""

Notable section seems to be: Proxy:<2010CASFQDN>:993:SSL;Proxy:<2010CASFQDN>:9933:SSL"".

First, there are two "Proxy:" entries showing. During normal and successful proxy connections, there is only one: 

014-08-05T19:46:01.846Z,0000000000036771,1,<2013CASIP>::993,<LOADBALANCERIP>:59894,<USERID>,241,24,25,login,<USERID> *****,"R=ok;Msg=""User:<USERNAME>:<GUID>:<2010DATABASE>:<2010MBXFQDN>;Proxy:<2010CASFQDN>:993:SSL;ProxySuccess"";ActivityContextData=14..."

Second, the 2010 CAS server is not listening on port 9933 but on port 993 (and 143). As a matter a fact, even on all 2013 servers, ProxyTargetPort value is not 9933, so not even sure where this number comes from. In IMAP logs it only appears in this specific log entry.

Other that this particular user, other IMAP services and connections seems to be working for most people on 2010 and 2013. I believe IMAP settings are thus set up correctly and I have gone thought them extensively.

I'm not understanding why the proxy is deciding, in some cases, to proxy to 2010 CAS server on port 9933 (at the same time as 993) for this particular user.

Any insight would be appreciated. Thanks.

ST

August 5th, 2014 10:22pm

Hi,

Please make sure that the service "Microsoft Exchange IMAP4 Backend" is started on your Mailbox Server.

CAS Servers proxy IMAP-requests to Mailbox Servers on port 9933.

You can try to reboot the Mailbox server and check the result.

The same thread for your reference:

http://social.technet.microsoft.com/Forums/exchange/en-US/4cbb7a6e-c6d9-4a83-b305-336617205991/imap-error-no-connection-could-be-made-because-the-target-machine-actively-refused-it?forum=exchangesvrclients

Hope this helps!

Thanks.

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August 6th, 2014 3:14am

Hi Niko,

Thanks for your reply. Sorry if my message was unclear but our IMAP4 service is working for everyone *besides* this one user/mailbox and *only* occasionally - about 12-20 times a day when both 993 and 9933 ports are being proxied at the same time for this user's connection.

So yes, IMPA4 service is started on ALL Exchange servers, I can successfully telnet to it, and our CAS servers do not proxy to Mailbox servers via port 9933 because this port has been changed to a different value of the "ProxyTargetPort" parameter with set-IMAPSettings command. This value has been changed on all 2013 servers, and 2010 servers are set to port 143 for "ProxyTargetPort".

August 6th, 2014 4:19pm

I have the same issue as well... mine is a single server config directly on my AD (I know, not recommended) but easier for a home config and virtualized.

Anyway, often but not always I see my IMAP accounts asking for credentials and the same exact error in the logs, then w/o punching anything in and just hitting OK it succeeds. See the error then my success below. Running Exchange 2013 CU8 on 2012R2.

2015-09-06T05:07:16.448Z,0000000000000010,2,192.168.0.101:143,104.48.241.45:65322,user,60079,22,23,login,user *****,"R=""sbdk NO LOGIN failed."";Msg=Proxy:host.domain.COM:9933:SSL;ErrMsg=ProxyTimeout:PreAuthTimeout"
2015-09-06T05:07:16.448Z,0000000000000010,3,192.168.0.101:143,104.48.241.45:65322,user,0,0,0,CloseSession,,
2015-09-06T05:07:35.203Z,0000000000000015,0,192.168.0.101:143,104.48.241.45:65383,,1,0,53,OpenSession,,
2015-09-06T05:07:35.228Z,0000000000000015,1,192.168.0.101:143,104.48.241.45:65383,,1,15,130,capability,,R=ok
2015-09-06T05:07:35.499Z,0000000000000015,2,192.168.0.101:143,104.48.241.45:65383,user,277,22,26,login,user *****,"R=ok;Msg=""Proxy:host.domain.COM:9933:SSL;ProxySuccess"";ActivityContextData=f7e2f11e-b01f-4946-af53-46199103c76d"
2015-09-06T05:08:14.658Z,0000000000000015,3,192.168.0.101:143,104.48.241.45:65383,user,0,520,34188,proxy,host.domain.COM:9933:SSL,


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September 6th, 2015 2:56pm

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