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When a Microsoft Exchange Server 2007 user sends a meeting request to external recipients by using Microsoft Outlook Web Access (OWA), the Message-ID of the meeting request is a unique GUID. For example, the meeting-ID uses the following format:
<GUID>@<FQDN of mail server>
However, RFC-2822 recommends that the Message-ID should use the following format:
[CFWS] '<' id-left '@' id-right '>' [CFWS]
Because of this incompatibility, the meeting request from OWA may cause a Non Delivery Report (NDR) message is generated by the external target mail servers sometimes. A specific NDR in this scenario includes the following message:
553 5.0.0 Message-Id header line format error
To resolve this problem, install Update Rollup 8 for Exchange 2007 Service Pack 1. For more information about Update Rollup 8 for Exchange Server 2007 Service Pack 1, see the following Exchange Help topic: