dovecot - Feb 2015 - Dovecot fsync question

Hello,

I followed these steps in http://wiki2.dovecot.org/MailLocation/LocalDisk

# Default to no fsyncing
mail_fsync = never

protocol lda {
 # Enable fsyncing for LDA
 mail_fsync = optimized
}
protocol lmtp {
 # Enable fsyncing for LMTP
 mail_fsync = optimized
}

This gives quite a good performance, but I'm not sure about the risks. Does
it mean that things like

*put a Sent Mail to Sent folder
*change status of mails

really don't get synced to disk for a long time (hours??). Or do we talk
about seconds and everything is fine when dirty pages get synced by the system.

cat /proc/meminfo | grep 'Dirty'
lets me assume that there are always just a few KB in the dirty pages and these
are written to disk every few seconds. Are the dovecot "mail_fsync =
never" transactions inclduded there?

Thanks a lot!
Christian