Allow inbound Port 25

Internet access discussion, including Fusion, IP Broadband, and Gigabit Fiber!
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by dkurn » Thu Aug 11, 2011 3:22 pm
Currently, sonic.net prevents both incoming and outgoing traffic on port 25. The reasons for this are probably:

OUTBOUND: Many spam-bots which infect the computers of unwary customers, send spam e-mails. These go out on port 25. Sonic is quite correct in preventing outbound port 25 from exiting their network, or working between computers inside sonic.net. I have no issue with this.

INBOUND: Sonic.net also prevents this. When queried about the reason, I got the explanation from Karen @ support:

This is to prevent "reflection" attacks which use the inbound port 25 to fool other servers into connecting to your server as they use their own server to send out the spam making it less taxing on their spamming server.

It took me a while to decypher this response. "Reflection attacks" (according to google) all involve a challenge-response protocol, but simple SMTP protocol on port 25 is not a challenge response protocol.

I therefore suggest that port 25 be opened inbound from the external network.

Anyone who has software listening to port 25 is probably not your "mom-and-pop Windows user". Setting up a mail server is a non-trivial thing. My Linux mail server, for example, was working for ten years on Comcast and ATT with lots of spam coming in, but various tools on my Linux box prevented damage.

The reason I want to run my own mail server is:
- I control what names are in use
- I control what domains I want to accept mail from, and also control the MX records that make it happen
- I don't want to use Sonic's mail server; it bothers me from a privacy perspective that my mail is stored on another computer, rather than "passes through".
- As a recent convert from ATT/DSL, they allowed port 25 inbound, and seemed to have no problems.

I know that Sonic.net will allow inbound port 25 to static IPs, but my IP is dynamic and has always been. Converting to a static IP could make Sonic.net non competitive in price.

I invite a discussion, because perhaps I haven't articulated my case properly, or may have forgotten some factor.

David (linux amateur in San Francisco, very happy with Sonic so far)
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