Fsync MTA option

File format MTA options: (0 or 1)
RESTRICTED.

The  MTA option may be used to cause the MTA to use the fsync function (UNIX)  to flush disk output when closing a message file. If such flushing is not performed explicitly by the MTA, it is left up to the O/S to perform on its own timetable; potentially, if a system crashes at just the wrong moment, messages not yet synched to disk could be lost. The tradeoff, however, is that performing explicit flushing for every message incurs a performance penalty. , meaning that flushes are performed explicitly by the MTA, is the default, ensuring message safety at the expense of a performance hit.

For the Message Store, somewhat analogous is the former store option  (default 15),  and even more so the newer   store options such as    (not advisable to set, other than in the special case of restoring from backup, per the iMS 5.3 Migration Guide).

See also:
 * File format MTA options
 * diskflushinterval Store Option
 * messagesynclevel Store Option