spamming from user by hidding domain name

Refer the solution given below:-

It seems that some user is spamming from your server,then for quick action clear the exim mail queue.

'rm -rf /var/spool/exim/input' 

It will do it, But you should investigate more & find the source script or domain & take actions so as to really help you out of this kind of issue.

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Fire the below mentioned command at your command prompt to find the domain which is being used by spammers for spamming.

# exim -bpr | exiqsumm -c | head

And Then,

#exiqgrep -ir <domain> | xargs -n1 exim -Mrm

That should remove any Email that is in the queue that is waiting to be delivered to POP accounts at [domain].