All Email Security Gateway, all firmware versions.
As a protection against spam and the abuse of distribution groups, Microsoft implemented sender authentication and restriction capabilities in Microsoft Exchange 2007. This setting is enabled by default for all distribution groups and dynamic distribution groups. This setting will function as designed with the Email Security Gateway: only internal, authenticated users will be able to send to protected distribution groups. If you wish to enable unauthenticated or external users to send mail to a specific distribution group, take the following steps:
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