It is possible that email addresses of the form email@example.com will create a directory in Gordanooutdomain.comuser where the directory domain.com already exists.
It is also possible to create directories such as tempuser with an address of the form user@domain/../../temp/user again only where the directory temp already exists. This will be a directory only, it will not contain any files.
The smtp service can be protected from creating these directories by adding the following 2 entries to the redirect file:
* * *@*/* * T F "500 invalid email address" * * *@** * T F "500 invalid email address"