[Mimedefang] best practices for handling filename extensions

[Bill Cole]

On 5 Oct 2017, at 8:04, Mark Coetser wrote:

> Pretty sure the filetype matching is done by checking the actual mime 
> type of the file not just what the file extension is, so just renaming 
> the file will still not allow the file through.

The file "examples/suggested-minimum-filter-for-windows-clients" in the 
source distribution which is the ancestor of many users' 
/etc/mail/mimedefang-filter matches by filename extension only. This 
actually makes sense for Windows clients, where (at least historically) 
the filename extension is the only indicator known to the OS of what the 
filetype is.