The following words are reserved and can't be used as the email addresses of groups you create in Google Groups:
You can use reserved words as email addresses when you create groups in the Admin console.
About abuse and postmaster
Abuse and postmaster are handled differently than other reserved words. When you create groups with the email address abuse or postmaster in the Admin console, you get the following message, "Settings weren't saved because an error occurred." The groups are still created, however, and they appear on the Groups list in the Admin console.
If you attempt to change the settings for groups with abuse or postmaster email addresses, you receive another message. "Group settings could not be updated. Please try later." You get this message because you can't change the settings of groups with abuse or postmaster email addresses. You can only add or remove members, and subscribe to email from these groups.