Answer
GMS has just received a message from another server that supports Enhanced SMTP (ESMTP). The remote server told GMS what size of message to expect but got it wrong! On other message servers this could cause problems if they commit a specific quantity of file space for the message to be delivered to.
In this case, session Undefined is processing a connection from Undefined which was processing email apparently from Undefined for Undefined (if there are multiple receipts for the message, this is the first recipient). The system at Undefined quoted a message size of Undefined but the message delivered was Undefined.
No action is required by you, GMS will process this message correctly. However, it would be advisable to contact the owner of the server/client at Undefined and suggest that they upgrade their messaging software to a version with this bug fixed or install an Internet Standards compliant messaging server so that they don’t affect other recipients of their mail.
See Also:
Keywords:SIZE ESMTP RFC1870