Architecture

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As one can imagine, processing all the incoming messages through anti-spam filters is a rather burdensome operation. If not tackled in the proper way, it can slow down all the email processing.

For this reason, at the beginning of 1998 we moved the spam filtering function to dedicated servers, called boundary servers, which process all email coming from outside, perform the filtering, and then distribute all the unrejected messages to the appropriate internal server. The whole filtering tier is composed by balanced clusters of mailservers: this means that we can spawn new cluster members at any time in order to redistribute the load across a wider pool of systems and be able to manage traffic spikes.

By internal servers we mean the machines our users are interacting with in order to send and fetch mail. These servers are not accessible via SMTP from the outside network, and they do not need to be burdened with filters: therefore, performance in message shipment and downloading is optimal. They exchange mail coming from or directed to the outside network exclusively with the boundary servers. Servers owned by our customers are also considered as internal, and are therefore protected by our external servers.

Spin has been one of the first italian ISPs to adopt a multi-layer architecture to implement an effective protection from spam and viruses without negative effects on the global performance.