Message-ID email header

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Hi . i am fetching messages from different mailboxes. Can same message that is sent to 2 mailboxes can have a different message-ID depending on the mailbox it is sent? I need to remove duplicates that have already been imported from 1st mailbox.

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Generally Message-ID must be unique - no two different messages must ever have the same Message-ID value.

Message-ID header is generated by the client program sending the email.
As you probably realize, email client can put any value as Message-ID and this can't be checked or validated. This means, that at least in theory 2 different emails may have the same id.

Having said that, I've never seen such situation in real live.

Emails with no Message-ID are more common.

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