At the moment, MaildirTempDocument() uses mkstemp() to get a unique filename in the temporary mail area.

This is probably wrong: we need to turn this into two functions. The first to return a file handle to a temporary file, the second to link something into the temporary file name.

It's not overly problematic I can see - it's likely not a security issue either - but it's slightly more work than we need to do.

We can probably lose mkstemp() as well, and do it more maildir-like.