(re-) dsync: INBOX Can't be deleted

[PGNet Dev]

> 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.