The stripped-down SMTP listener a content filter reinjects already-scanned mail into.
Also unregistered with IANA. In the standard amavis setup, master.cf runs a second Postfix smtpd on 127.0.0.1:10025 with most checks disabled, and amavis returns clean mail to it via $forward_method='smtp:[127.0.0.1]:10025'. Postfix's own FILTER_README documents the same sandwich with a 10025/10026 pair. A probe sees an ordinary Postfix ESMTP banner, which makes the port easy to mistake for a legitimate public MTA.
Do not expose
This listener deliberately runs with relay restrictions and receive overrides removed so that filtered mail passes unchallenged. Reachable from the internet, it is a literal open relay — bind it to the loopback interface.
$ printf 'QUIT\r\n' | nc -w 3 127.0.0.1 10025Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.