I have copied a number of my old sent items into Zimbra's sent folder using thunderbird with imap. Logging into Zimbra I can see all the mails in the sent folder however in the message list the to address is listed as my name. Selecting one of the messages shows that it still has the correct recipient listed in the To header. Even more strangely if I hover over my name in the list, the popup that appears shows the correct recipient.

Additionally the mails don't look like sent messages, they look like normal read messages.

Is there anything I can do to correct this?