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Avoid "reinventing the wheel"...
It's possible to obtain high-availability mail through less-complication means.
There are some redundancies already built into the SMTP protocol (retries, MX priority, etc.). You can get much of the same protection by using a backup MX that can spool if your primary delivery system is unavailable.
IMAP does what you're asking in terms of synchronization. Microsoft Exchange MAPI is a little more elegant.
The path of least resistance (and $cost) is probably obtaining an account on a hosted service, for example, hosted Microsoft Exchange available through any number of cloud providers. Let them handle the redundancy. It doesn't have to be Microsoft. There are plenty of Linux-based mail hosting solutions available, too.