When you go to send your message, Direct Mail may warn you that one or more attachments are missing. This means that Direct Mail is not able to locate the file that you originally attached to your message.
Direct Mail may be unable to locate the attachment because it has been moved or deleted since you first attached it, or bad file permission prevented Direct Mail from accessing the file.
You can fix the problem by removing and reattaching the files from your message. How do I attach files to my message?
Starting in version 4, Direct Mail will make a private copy of files that you attach and store that copy inside the project itself. This greatly reduces the odds of missing attachments or other related problems.