My server sending mail but no user connected! :?

[TitusI]

Hi,

big trouble here, I'm migrating a server, zimbra 8.0.6, due to my concerns on security and other reasons.
I'm still configuring it, but one think really set me on concern!

I've migrated user and email, but user are still using the old server...but into the daily report I see "a lot" (for an unused server) of transiting mail...

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

808 received ---> (? when the old server is down I suppose)
1734 delivered ---> (too mutch!!)
0 forwarded
9 deferred (140 deferrals)
16 bounced
214 rejected (10 %)
0 reject warnings
0 held
0 discarded (0 %)

2588k bytes received
6099k bytes delivered
644 senders
502 sending hosts/domains
91 recipients
9 recipient hosts/domains

the DNS still point to the old server, but there is a MX record for the new server.
So now I'm really on concern, what to check?

[TitusI]

Any hint?
Do you need other information?

[Raun]

In the same report you would see the account that sent out the most number of emails. Start from that and the check zimbra.log for any anomalies .

[TitusI]

Thank you,

allready done, it's an unexisting user (how to avoid zimbra sending message from unexistent user on the server?)
The server is the second listed (priority 70 versus priority 30 of the worcking mail server) in the MX record
The other server never went down.

mail.domain.com point to the actually working old mail server ip