Symptom
When sending an email working in Daylite, you receive the following error: 
Why is this problem occurring
This error comes up when the email message you are trying to access cannot be found in Mail.
Solution
This error indicates that Daylite is attempting to search for the original Email from your Apple Mail Inbox, but it cannot be found due to one of the following reasons:
- The email was removed, archived, or deleted from Mail. It may have been deleted or not downloaded from the Mail server.
- The email message ID is encoded differently due to an operating system upgrade.
- The Mail server account has not been set up.
You would still be able to view these emails within Daylite, but you would not be able to use this function to retrieve them from Apple Mail if it had been deleted in Mail after adding it to Daylite through the Daylite Mail Assistant.
To resolve this issue, the original email would need to be made available again in your Apple Mail inbox and then linked back to Daylite again in order for the 'Show in Mail' feature to work successfully.