[Mailmunge] Spool Ram Drive

[postfix at ptld.com]

> The odds of getting MX_MAXIMUM maximally-sized messages all at once
> is pretty darn low.  The theoretical maximum would actually be roughly
> twice this, because mailmunge decodes the MIME parts into the RAM disk
> as well as storing the original messages.

What does happen if the ram runs out of space? I assume something along 
the lines of a file open error. What does mailmunge do? Crash the 
worker? Trap the error? Allow the email, temp fail, etc?