Open Mail and go to the Inbox
Launch Time Machine
As Time machine does a backup every hour, you can step back in time, using the indicator on the right, until you find the missing email.
Select the missing email and click Restore.
That should pull the missing email back into the inbox.
Have you checked your deleted folder to see if it is still in there?
I managed to delete an important email whilst tidying my mail, is there any way to grab/merge an older mail Archive? via Time Machine? my machine is regularly backed up through Time Machine...
One way I thought was to restore my machine to date before the email was deleted - then restore back to the present state - but this seems a long and slightly dangerous route? is there not another way?
many thanks Kieran