Whenever I try to delete old email in the Sent Items folder, I receive the error, "The Messaging Interface has returned an unknown error. If the problem persists, restart the computer."
I ran the inbox repair tool, but that didn't work. I also created another pst and transferred some folders there, because the user was close to her 2GB limit, but that didn't help either. I don't know what else to do. Any help would be appreciated.