Quoting Timo Sirainen <tss@iki.fi>:
It depends on the locking scheme used by the filesystem. Working queue directories (the ones where stuff comes and goes rapidly) is best suited for a local FS anyway.
And when a server and its disk dies, the emails get lost :(
It would appear he is not talking about a /var/spool/mail type queue/spool, but the queues where the MTA/AV/Anti-Spam/etc process the mail.
For the most part, on machine crash, this will always result in the mail being lost or resent (resent if it hasn't confirmed the acceptance of the message yet). If done with battery backup, the risk is less, but since most filesystems (local or remote) cache writes in memory, the chances you will lose the mail is high in any case (if still cached in memory).
I agree that for smaller mail systems, the processing queues are best on local fs or in memory (memory for AV/Anti-Spam, local disk for MTA processing). The delivery queues (where the message awaits delivery or is delivered) are best on some other file system (mirrored, distributed, etc).
For a massively scaled system, there may be sufficient performance to put the queues elsewhere. But on a small system, with 90% of the mail being spam/virus/malware, performance will usually dictate local/memory file systems for such queues...
-- Eric Rostetter The Department of Physics The University of Texas at Austin
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