I am running Outlook 2013 Professional and we have Exchange 2010. 

Periodically when I am deleting messages I receive a box that says "Unknown Error" it doesn't say anything else and if I click OK it goes away... its more of an annoyance but we are going to start using 2013 more often and I want to see if anyone has any thoughts on the cause.

Thanks

Hi,

I would suggest to try the methods list in the article below:

http://www.howto-outlook.com/faq/deletemessage.htm

Best regards,

That is not really an answer.

This is occurring on select Outlook 2013 clients (more than one), connecting to on prem Exchange 2013. The behavior is exactly as Jessica describes above.

Does anyone have any further info on this? Something new from this year? (2014)

I can reproduce this issue by deleting several emails in a row from the Outlook client. I also have two other users that can reproduce it with the same behavior. We are all on the same environment (as I describe above). Exchange and Outlook are both 2013, SP1. I have also installed the April 2014 hotfix package for Outlook 2013 - that did not resolve the issue either.

Here is what really stinks. I have Premier access, and even that has no information related to this issue or anything similar.

Any fix yet?  Just updated to CU6, same issue persists.

Just curious if anyone using 365 has the same issue?

Seemingly this error occurred as far back as 2003, my guess is whatever fixed it in the past doesn't work due to extra integration with the CAS server, MAPI over HTTPS or whatever its called today.

Hi, 

We also experienced the issue on Outlook 2013 on our terminal server. Whenever a user trying to delete multiple emails real quick it gave the Unknow Error.

Some users suggested to use cached exchange but we do not want that solution as we are on the terminal server.

i would suggest you o have a look on this thread it will help youto resolve this unkown error

https://social.technet.microsoft.com/Forums/en-US/ed6717af-235f-457d-93d3-a1f1a36936a3/operation-failed-the-messaging-interfaces-have-returned-an-unknown-error?forum=exchange2010

Regards