You reach this tab by going to Settings –> Spam Filter -> General, and then choose the General tab.

The Spamfilter script has various settings that can be changed to alter the behaviour of the spamfilter. These are defined in the script, so may change with different versions of the script. The settings are currently:

If this is 1 then the spamfilter will finish processing the incoming message early on if it finds that it is very likely to be spam. This reduces CPU load on the server, and speeds up the processing of messages

With the default setting of 0 the spamfilter starts some DNS requests at the start of processing the message, then checks the results at the end. This means that it isn't waiting around idly for the results.

If this is changed to 1 then the spamfilter will check the results at the beginning of the processing. This may slow down the actual processing time of the message (it is quicker if you have your own local DNS server on your network). However, it means that, in combination with the AllowQuickEnd setting above, the spamfilter could skip the majority of the checks if the DNS results show that this is likely to be spam - reducing CPU load.

This is most beneficial on a mail server with an incoming SMTP feed, as it may be receiving many messages at once. The individual processing time of a message is less important with incoming SMTP as well, because messages are received concurrently, rather than one after the other, as with POP3.