Just like many SFDC users, we not only have Marketo app syncing to SFDC but others as well. We use Linkpoint to send emails and create entries into Marketo. Anytime a lead opens an email, we have Marketo assign it 1 point.
The problems is, when that recipient opens the email, Marketo doesn't sync it to the existing lead. It creates a new MKtounknown and assigns the point there. It doesn't see that the email already exists. Is it because our sync time-delay was set infrequently? It happens to us numerous times a day.
By the way, the emails are identical so i don't know why it just doesn't sync.