So I mailed 10k emails but when I read this I can't tell how many were successful or not because the numbers don't seem to add up at all.

For example: if 6586 were successful then how can 7k be deferred or bounced?

My question: How many were successfully delivered?

Grand Totals
------------
messages

10102 received
6586 delivered
0 forwarded
3741 deferred (9741 deferrals)
3289 bounced
6 rejected (0%)
0 reject warnings
0 held
0 discarded (0%)

13202k bytes received
16534k bytes delivered
17 senders
66 sending hosts/domains
3221 recipients
2521 recipient hosts/domains

The mails can be still be successfully delivered even if they were deferred, e.g. by greylisting, throttling, etc.