spam to aliases and system accounts

[Daniel Pocock <daniel@pocock.pro>]

When people install Debian (or any distro), they usually get a bunch of
entries in /etc/aliases and various system accounts (/etc/passwd entries
with UID < 1000) created by the packages they install.

I've noticed an increase in spammers targeting some of the more common ones.

Can the number of aliases installed by default be reduced?

Do any of the mailers (postfix, exim, etc) provide a convenient way to
exclude delivery to system accounts by default, or to exclude these
aliases and accounts from receiving mail from external senders?  Could
anybody share examples of how they do it or pointers to any blogs or
wikis with examples?

Could/should any more be done at the packaging level to minimize this
problem or is it something that can only be done on a per-site basis?

Regards,

Daniel