Though the destination's email server accepts the email (during the SMTP session), this email is still possible to bounced back - some people call this as asynchronous bounce (rejected during SMTP session is called as synchronous bounce). Therefore, I would suggest rename 'delivered' to 'sent' as 'delivered' indicates that the message has been delivered to the mailbox of the recipient.

For our business, when I ask sendgrid to deliver a message to 10k people, I care about the deliverability metrics as below:

• Dropped - 100: how many dropped by sendgrid, i.e. sendgrid would not try to deliver the message due to some reasons such as invalid emails or people told sendgrid stop delivering to their mailbox or the email address has been bounced in a short period etc. 
• Sending failed - 400: sendgrid tries sending but rejected by the destination mail server (synchronous bounces)
• Sent - 9500: how many successfully sent out ( the destination's email server accepts the message, this indicates the delivery responsibility from sendgrid mail server)
• Bounced - 500: how many definitely not be able to deliver to the recipients notified after accepted by the destination mail server (asynchronous bounces, permanent failure, maybe hard bounce or giving up after repeated soft bounces)
• Spam reported: how many delivered but reported as spam by the recipient
• Inbox placed: how many delivered into the inbox instead of spam folder, not sure if it is possible to collect this.

What are people's experiences with using email reputation services while using sendgrid? Are services like ReturnPath beneficial to SendGrid users (assuming, of course, that spam isn't being sent, emails are formatted correctly, etc.)? It seems that the things that SendGrid does in terms of not emailing to addresses that have opted out, etc. should already work towards one's reputation, so I'm wondering how necessary those services are (and if anyone has a particular recommendation)..