[Dovecot] temporary disable account

Hello,

is there some way how to disable temporarily account or access to files. I need to backup with tar, but there is problem when tar is reading and some file changed (with --ignore-failed-read it continues but archive is not created and without --ignore-failed-read it fails). Some accounts are huge ;( Need something like qmail sticky bit or world writable directory - qmail is not delivering when one of above conditions hits.

Thank you for helping me.

Lampa