Strange enough, some of my mail domain external sender used to send us messages where Message-ID field set to $Null like this:

    Date: Tue, 1 Dec 2020 07:16:22 +0000
    Message-ID: $Null
    Subject: Test

(looks like this is due to Exchange + Outlook setup used in their company, but can't find more info).

This is a bit problem until recent times as Apple updated iOS mail client and recent Mail app in iOS messed up all messages list when try to analyze such a message.

The fix I try to implement is simple, I try to add this action to Exim's acl_check_data:

      condition               = ${if eq{$h_message-id:}{\$Null}}
      remove_header           = message-id : message_id : Message-ID : Message_ID

I tried many ways of referencing Message-ID header line but even that condition yields to true the "remove header" action won't remove the Message-ID header line.

So please advice, how can I remove or (better) replace broken header line of Message-ID with some correct value?

  • Hi, is there any update? Please check if the below info is helpful to you. – Ivan_Wang Dec 23 '20 at 8:37

Sorry for that i'm not familiar with Exim, however, I found a documentation about the message-id in Exim for your reference, please check if it's helpful to you: Message processing(The Message-ID: header line)

Did you deploy an Exchange server for your accounts? If so, you could create a transport rule to modify the message-id in the message header according to the conditions:enter image description here

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