Obtener datos sin marcar de db

DECLARE @teamName varchar(50) = 'TEAM01'

SELECT * 
FROM Mails M
LEFT OUTER JOIN MailAssignments MA ON M.msgId = MA.msgId
WHERE MA.msgId IS NULL OR 
      (
         MA.forTeam IS NULL AND 
         MA.notForTeam <> @teamName AND 
         MA.processedByTeam <> @teamName
      )

¿Haría esto lo que quieres?