from yesterday, when I login to admin UI, I found these's always thousands of mail in mail queues,both deferred and active, and the sender and receiver are not my domain.

where these mail come from? how to stop dealing with these spam?

I do these things below, but do not take effect
1. change ssh password
2. disable ssh port
3. lock all user in zimbra except admin
4. disable all port except 25/80/7071

thx for any help