You use the Set-SenderIDConfig cmdlet together with the BypassedSenderDomains parameter on a Microsoft Exchange Server 2007 server to exclude domain names from the Sender ID filter. In this situation, this setting may not take effect if the senders' domain names include capital characters. For example, you run the following command in Exchange Management Shell:
If the sender is <someone>@contoso.com, the message is delivered without the Sender ID filter. However, if the sender is <someone>@Contoso.com, the message passes through the Sender ID filter and may be rejected.
Set-SenderIDConfig -BypassedSenderDomains "contoso.com" -SpoofedDomainAction Reject
This problem occurs because domain names that are in the Bypassed Sender Domain are case-sensitive.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.