Postfix - Odd emails creating too much traffic
I was using Postfix without any problems but last two months time the traffic usage of the server is increased too much. When I checked the mail queue I see emails for an account which does not exist on my server. Below is an example how the mail queue looks like. I checked for open relay both manually and some online sites. There's no open relay.
It causes too much traffic. And I see 60 to 700 messages in queue.
messages in the queue are like:
(delivery temporarily suspended: connect to mx1.likya. com[192.168.255.255]:
Connection timed out)
Is this a kind of spam method? If yes, could anyone give me an idea how to fix it? Please help.