I believe that this feature will assist to prevent undeliverable mails to postmaster.
Path: Tools > Manage Email Accounts > Edit Account > New Item Settings
Fill in the free text field "Ignore messages where the subject contains"

What is the format for the entries in to this field and what are the separators, please?
Will the following work:

postmaster;
out of the office;

Relates to post http://community.axosoft.com/forums/thread/12028.aspx