[Dovecot] Mixing MBOX and Maildir?

[Marc Perkel]

Is it possible to have some folders be mbox and some be maildir format?

Why you might ask? Sometime for diagnostics I have the Exim MTA archive 
certain messages in MBOX format and then I want to copy them into an 
imao folder to look at them with Thunderbird. When I used MBOX all I had 
to do was copy the file into a folder and it worked. So what I'd like to 
do is have a folder with a special name that is MBOX and the rest be 
maildir.

Ideally have Dovecot be smart so that if the file exists then it is 
assumed to be MBOX and if the directory exists then it is assumed to be 
maildir. Has anyone done anything like this?