I am trying to secure my droplet to prevent too many emails being sent out possibly my malicious scripts that get injected to the server. I know one option would be to monitor the logs and when a certain limit is exceeded per hour I get notified by email but I would like to know if there is a way to set limits to how many outgoing emails can be sent by the server or for a way to restrict outgoing smtp to only specific users i.e. exim, sendmail and root.
I have a droplet with Ubuntu 14 and Exim4.
Any help would be greatly appreciated. Thanks
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