This depends upon load on the server. In this case request is to check monitoring logs and check on the status of deliveries from the same. If the same is delivered it corresponds to delivered and wait for some time to check on the change to status in the deliveries.
When our MTA gets an email, it goes to the MX server of target domain, informing them of the new email to be delivered.
The MX server accepts the email and then gives us an acknowledgement as success or failure with the response code.
It is this status which gets reflected in your delivery logs.
It is also the point till which Campaign has control. Beyond this point we cannot ensure deliverability.
One of the following things happened in yoru case.
1. Check if the email has landed in SPAM/JUNK folder as we normally wait for emails in inbox, while they are hidden in SPAM. If this is the case, fix the reason why it is going in SPAM. Check the content of your delivery.
2. If point 1 is not relevant, then a Sent status means MX server accepted the email and told us that it has been delivered. However, the same didn't reach the inbox because of internal company policies like spam checks, rule filtering etc.
For point 2, the MX team of the target domain needs to be contacted to fix the problem.