I think an option for mhonarc to avoid the directory listing
would be quite helpful, at least in my situation.
I would love to have access to the last message number after
a MHonArc run.
=v= I handle a similar situation like this: do a directory-wide
operation, then record the directory's modification date. Next
time around, check the directory's modification date and skip
the operation if it hasn't changed. In this situation, that way
you would know that the last message hasn't changed since the
previous operation, so you can skip the directory read.