<p>Well what value would you give it? I'm not even sure what generates the message IDs, ie whether rails does it or whether it leaves it for exim to do, but I am sure it doesn't record them anywhere so it has no idea what value to use in the future.</p>
<p>There's also no way to know which comment a future comment refers to, so would you just have all comments as replies to the original entry? But that never has a message ID at all because no email was ever sent for it... Even if we invented one I'm not sure what a mail client would do with a bunch of messages that claim to reply to a message it has never seen?</p>

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