Those of you who have already installed the latest Rollup for Exchange 2010 SP2 Rollup 6 or SP3 may face a problem regarding deleting emails from mailboxes.
After installing SP3 or RU6 for Exchange 2010 SP2 users can have a problem with deleting emails from inbox folder.
When you try to delete email you can receive error message: “unknown error” and, of course, email is not deleted.
A lot of users wrote on Technet Forums that this issue occurs when you try to soft delete email from inbox folder, especially when email contain an attachment such as: PDF
Interestingly the problem does not occur when you delete an email using Shift + Del or when you move this email to other folder or subfolder.
Another interesting fact is that this problem only occurs in Outlook online mode and OWA. However, in the Outlook cache mode no problems.
Unfortunately, the solution for now is to uninstall the installed updates RU6 for Exchange 2010 SP2 or uninstall SP3.
Several problems are reported to Microsoft, which confirms that receives such notification but not yet officially on the subject is not spoken.
English 
polski