On a SQL Server 2008 (SP3) Express Edition I tried sending an E-Mail using the Database Mail feature. I kept getting an error message in the Server Logs (use Management Studio and browse to Management\Server Logs in the Object Explorer on the left side) when trying to send an E-Mail:

Exception Type: Microsoft.SqlServer.Management.SqlIMail.Server.Common.BaseException
Message: The read on the database failed. Reason: Fehler beim Laden von 'Msxmlsql.dll'.
Data: System.Collections.ListDictionaryInternal
TargetSite: Microsoft.SqlServer.Management.SqlIMail.Server.Objects.QueueItem GetQueueItemFromCommand(System.Data.SqlClient.SqlCommand)
HelpLink: NULL
Source: DatabaseMailEngine

I could resolve this issue by coping the files …\Microsoft SQL Server\msxmlsql.dll and Microsoft SQL Server\Resources\1033\msxmlsql.rll to the SQL Server instance folder Microsoft SQL Server\MSQL10.[INSTANCE]\MSSQL\Binn.