using variables in muttrc

[Louis-David Mitterrand <vindex+lists-mutt-users@xxxxxxxxxxx>]

Hello,

All my mailing list subscriptions are done from a "plussed" address: 

        <login>+lists-<listname>@domain.tld 

It eases list filtering at the procmail level but raises an issue when
replying to mailing lists as they require the From: to contain the exact
subscription address (even though the extension after the + shouldn't be
considered part of the address per se).

So I am trying to build a send-hook that inserts the correct "From:"
address:

        send-hook '~l' "my_hdr From: vindex+lists-$FOLDER@xxxxxxxxxxx"

When browsing the imap://host/INBOX.mutt-users folder I'd like the
send-hook to substitue $FOLDER with the string "mutt-users".

Is there a way to make that work?

Thanks,

-- 
ldm@xxxxxxxxxx