Translations:Complete Virtual Mail Server/amavisd spamassassin clamav/9/en

Spam-assassin and ClamAV are the tools to block spam and viruses, however amavis is required to tie this all together. Amavis will actually behave as a mail server in itself, accept mail, filter it, and send it onwards again. For this to work, postfix will need to actually listen for mail twice. The default port 25 is where mail initially is received on. From there on it is sent to amavis, which will be listening on port 10024. When amavis is done with the message, it will be sent to postfix on a different port, 10025. The reason for this should be obvious. If mail would be offered again on port 25, it would be passed to amavis again and thus in an endless loop. Obviously, postfix on port 10025 would only be listening to known hosts, like localhost and not check for spam anymore.