From: Phil Howard on
On Wed, Jun 9, 2010 at 02:43, J. Roeleveld <joost(a)antarean.org> wrote:

> Even though I have considered it myself as well once, I am curious as to why
> someone would put a firewall on localhost?

Other applications could become compromised by spammy virii that
exploited their vulnerabilities and start spewing filth, either by
direct connections, or by connections to the local mail server. Of
course, running the sendmail command is yet another option.