I was setting up Mail on a new machine, and could not see all of my messages on the new machine. I thought there was an issue with syncing the mailboxes to the new Mac, as I have many folders and many messages, but the issue turned out to be that the Message Filter was enabled on the new Mac. Since this cost me a couple of hours trying to resend and even using Onyx to rebuild and even delete the email msg index.
This may be common knowledge to many, but since it happened to me (and I have used Macs since 1984), I post this as a public service.
After noticing it was only the read message not appearing, I found the solution here Mail not showing read email and all was normal. It is a mystery to me how that filter got set on the new Mac, but likely "operator error" as I do not recall ever using this feature.
The Message Filter is accessed by clicking that little icon (circle with lines) at the left of message preview window:
![Message Filter.png]( "Message Filter.png")
This may be common knowledge to many, but since it happened to me (and I have used Macs since 1984), I post this as a public service.
After noticing it was only the read message not appearing, I found the solution here Mail not showing read email and all was normal. It is a mystery to me how that filter got set on the new Mac, but likely "operator error" as I do not recall ever using this feature.
The Message Filter is accessed by clicking that little icon (circle with lines) at the left of message preview window: