rImap

It is necessary in some cases to be able to use
different folder
names on different servers, because not all names are
valid on
all servers.

For example, one IMAP server I use, www.fastmail.fm, only
allows creation of new folders under INBOX, so all
folder names
end up looking like INBOX, INBOX.foo, INBOX.foo.bar,
INBOX.xyz,
etc. But IMAP at mac.com supports arbitrary folder
names, so I
can have folders foo, bar, foo.bar, xyz, etc. That
means I cannot sync
directly between fastmail and mac.com, because most of
my folder
names on mac.com aren't valid on fastmail.fm.

I'm not sure what the best solution is. In this
particular case, adding
a parameter that says to stick a prefix on all folder
names on fastmail
except INBOX would work, since I could set it to
"INBOX." and things
would work about as I would expect. I don't know if
that's general
enough for all cases, though.