No longer true? :From
https://www.fastmail.com/help/ourser...liability.html
Replication
When anything changes in your mailbox, such as receiving new mail, that change is immediately copied (or replicated) onto two separate servers. That way if a server fails, your mail is still accessible and secure.
These servers also write to redundant disk drives. If a disk fails, the system still runs, we get an alert, and the disk is swapped with a spare, with no downtime or loss of service at all.
If you want to know more, we've written
a detailed description of our storage and replication architecure.*** <sic> <=Note spelling typo.
Backups, just in case
Beyond the protection of our redundant live servers, we also maintain a backup system which takes nightly backups of all your email and mailbox activity. If any emails are deleted, the backup will keep a copy for up to 7 days.
This backup system is designed to function separately, and entirely differently, than the live system. It does not share any common traits in configuration or coding. Basically, if catastrophe strikes the live system, whether that be an advanced virus or a targeted attack, that attack will not affect your backed up data.
This is all highly unlikely, but we've planned for the worst to ensure that your data remains intact and undamaged.
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The log files, among other places, must have the autosaved drafts in 'em.
From the architecture.html file:
Replication
The Cyrus replication system doesn't record the actual changes to mailboxes: it just writes "something changed in mailbox X" to a log file (or in our multi-replica configuration, to a separate log file per replica).