I am trying to troubleshoot emails not being received by a customer. Under the contact I see that the user sent 1 email to the customer. However, in the log file I see 2 internal message id’s, 2 Deliveries and 1 Received. Am I to assume that the customer successfully received the email?
Not necessarily. The (R) event means that Salesforce’s mail server successfully received the message and the (D) is the record for the delivery. However, an unsuccessful delivery will also get an entry. Take a look at the Delivery Status Notification (column O) to see a status code for the log. Successful sends get a 2xx code. That said, a success code isn’t a guarantee the contact gets the email, just that it transmission complete successfully. It can still fail through later mail servers (if there is a proxy), or if it’s filter at spam at either the server level or the user’s inbox.
See the email log format help doc for additional information on interpreting email logs.