Name: expunge_mode
Type: ENUM
Allowed-Values: immediate semidelayed delayed
Default-Value: delayed
Last-Modified: 3.1.1

The mode in which messages (and their corresponding cache entries) are
expunged.  "semidelayed" mode is the old behavior in which the message
files are purged at the time of the EXPUNGE, but index and cache records
are retained to facilitate QRESYNC.  In "delayed" mode, which is the
default since Cyrus 2.5.0, the message files are also retained, allowing
unexpunge to rescue them.  In "immediate" mode, both the message files and
the index records are removed as soon as possible.  In all cases, nothing
will be finally purged until all other processes have closed the mailbox to
ensure they never see data disappear under them.  In "semidelayed" or
"delayed" mode, a later run of "cyr_expire" will clean out the retained
records (and possibly message files).  This reduces the amount of I/O that
takes place at the time of EXPUNGE and should result in greater
responsiveness for the client, especially when expunging a large number of
messages.
