> hints/suggestions as to what?
for anyone interested, the causal issue is NOT directly the one reported in the
non-verbose output
Error: Mailbox INBOX sync: mailbox_delete failed: INBOX can't be
deleted.
rather, the relevant 'hint' is the
Debug: brain M: Mailbox INBOX: ... GUIDs conflict - will be merged later
message seen only in the debug output.
In addition to
rm -rf /data/vmail/example.com/testuser/Maildir
clearing the index data, configured here in a separate tree,
rm -rf /var/vmail-index/example.com/testuser/*
does the trick.
backup, now, appears to complete.
