Outbound Port 25 Blocking is a measure to prevent virus-infected computers and senders of unsolicited emails (spam) to send large volume of emails from their PC or server without using the providers outgoing mail server intentionally/unintentionally. Providers in the US and Japan are implementing this configuration.
Generally, Port 25 is used to send this type of spam mail. By implementing Outbound Port 25 Blocking, we restrict any communications from port 25 to non-Asahi Net mail servers and prevent sending of spam mail using Asahi Net's internet connection services.