An electronic mail message (EMM) addressed to a distribution list of an enterprise is received at a server of the enterprise from a sending address outside of the enterprise. If the distribution list has no external addresses, then the EMM is blocked from being delivered to the distribution list. In an embodiment, if the distribution list has an external address and the sending address is identified in a safe sender list corresponding to the distribution list, then the EMM is delivered to the distribution list. In an embodiment, if the distribution list has an external address, the sending address is not in a safe sender list corresponding to the distribution list, and the content of the message is approved, then the EMM is delivered to the distribution list.