The message ID header is missing from some email messages that arrive at my server

Symptoms

You find that the message ID header is missing from some email messages.

Cause

Many email providers require this header before they will accept the email. Exim itself does not add, remove, or alter the message ID. The message ID is normally generated by the mail client. 

Resolution

If the mail client you are using is not generating a message ID header, it is recommended to use a different client. 

Additional resources

How to find email headers