There are several steps to using this plugin.

- Add the plugin 'postal'  to your setup file.
- Add the plugin 'mailbox' (packaged seperately)

- update your template(s).  See examples/page.tmpl. Look for POSTAL_DIV

- Manditory configuration

  + postal_prefix	first part of email address i.e. user-wiki-
  + postal_host		where to send the mail

- Optional configuration:

  +  postal_pagespec  what pages to add comments to.

- the script filters/postal-accept.pl takes a mail message on standard in 
  and files it in the appropriate comment box.

    perl -c path/to/my/ikiwiki-setup  < mail-message

This would all get somewhat easier if and when these plugins are 
distributed with ikiwiki.