Instead of copying the backup messages directly into my email account folders I used the import procedure. After that, I selected all messages and moved them from the imported folder to my account. And all the displayed information was correct and complete.
I tried before to use the import procedure but when the wizard asked for the location of the messages I wrongly chose the Sent items folder or the Inbox folder. This is not accepted by the wizard. Instead I should have chosen the account folder which contains the Sent items folder and the Inbox folder.
The problem occurred after restoring my email. The emails themselves are intact only the column Attachment is always empty for restored messages. For new messages the paper clip symbol is shown. Because I was used to OE I just backuped the Sent and Received folders not aware of hidden files. So I could not restore the file with meta information named Mail.MSMessageStore. Trying to solve the problem I removed WLM and reinstalled it. Then I copied the messages to there folders. The Mail.MSMessageStore was present again but the problem was not solved. I think the same applies to other columns like priority and flag but I rarely use them. I am using Windows 7 and I don't have an old version of the Mail.MSMessageStore file. Does anyone know a way to get my email list complete again?