Hello to everyone

can someone help me with this report?

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

421 received
489 delivered
0 forwarded
5 deferred (5 deferrals)
2 bounced
7962 rejected (94%)
0 reject warnings
0 held
0 discarded (0%)

86824k bytes received
106093k bytes delivered
89 senders
70 sending hosts/domains
68 recipients
40 recipient hosts/domains

I think something cant working well.what does that means about rejected?

Another question in report is :

RCPT
Helo command rejected: Host not found (total: 7766)
5978 domain1.com
1389 mx.domain.net

My zimbra reject this domains?

And the lastone question is

top 50 Senders by message count
-------------------------------
79 user1@mydomain.com

What does tha means?This user1 in this case was send 79 emails??

thanks a lot.