It seems that my server is being used to send out spam mail. I first recognised this as an issue as the memory spiked and the mail.log file is absolutely huge! Looking at the logs there is a lot of errors / email addresses that I don’t recognise. For now I have disabled Postfix and the memory use has dropped considerably (the majority of sites on my server use SMTP mail anyway) but how would I go about debugging this? Would I be able to find the cause?
Ubuntu 16.04.3 x64 - happy with terminal commands
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