Please let me know if anyone knows an answer to this one... We're in a Hybrid Exchange environment, with 2 x Exchange 2007 servers, and 1 x Exchange 2013 Hybrid server which is pointing to Office 365 for the purposes of relaying mail to O365 while we migrate our users out there.
We have just finished migrating, but just a couple of days ago we started experiencing delays in email delivery to O365... Not all mail, but some! Incoming email or locally generated email gets relayed out through the Hybrid server and out to O365, but not all email is delayed... only some, but it's constant. During the busiest part of the day, about 200 messages are sitting in the Queue in Exch2013... but they all eventually resolve between 5 and 45minutes. The users are not happy.
The last error in the queue viewer for each hung email reads: 451 4.4.0 Temporary server error. Please try again later.
If I look at the message tracking logs, I find an interesting item -- "RecipientThreadLimitExceeded":
2014-05-15T14:15:51.608Z,192.168.3.11,hydra,207.46.163.215,company-mail-onmicrosoft-com.mail.protection.outlook.com,RecipientThreadLimitExceeded,Outbound to Office 365,SMTP,DEFER,10307921510617,<5E5E05B0073A514AA6D072AFB5EB8182276370A4@APSWP0475.fubar.com>,885ea3ce-a020-41b1-8950-08d13e58d6d3,JoeUser@company.mail.onmicrosoft.com,451 4.4.0 Temporary server error. Please try again later,10117,1,,,Read: This is your generic subject line,sender@fubar.com,sender2@fubar.com,2014-05-15T14:16:51.608Z,Undefined,,,,S:Microsoft.Exchange.Transport.MailRecipient.RequiredTlsAuthLevel=Opportunistic;S:Microsoft.Exchange.Transport.MailRecipient.EffectiveTlsAuthLevel=EncryptionOnly;S:DeliveryPriority=Normal
I have tried to find some documentation on resolution for this RecipientThreadLimitExceeded error, but I can only come up with some Exchange 2011 documentation which recommends adding some entries to the EdgeTransport.exe.config file to bump up the RecipientThreadLimit value... I have not found anything pertaining to 2013. I cannot even find any powershell commands to see what the current RecipientThreadLimit is on 2013! Aghg!
Has anyone seen this before, or have any recommendations?
Thank you,
Mike