mail server DNS configuration questions
kdk at daleco.biz
Thu Sep 11 02:44:09 UTC 2008
Andrew Falanga wrote:
> Clients in the churches private network cannot send mail using this
> server, though they can receive mail from it (POP). The church has a
> private network, PN1, and the mail server sits at a church members house
> because he has a static IP address; let's call that PN2. The router at
> his house is setup to forward traffic over port 25, and the POP port, to
> this server. Also, just to further clarify, the Internet separates
> these two Private Networks. However, this may not be entirely true as I
> think about it because at both locations, the ISP is CableOne using
> cable broadband. So, though technically part of the Internet, the
> traffic shouldn't leave the CableOne domain. Also, of interest, is that
> another of our pastors uses CableOne at home and is unable to send
> e-mail using the churches server from home. However, from a coffee shop
> in town, that our pastors frequent, they are able to send mail. It is
> my understanding that this coffee shop does not use CableOne.
> So, just to make sure everyone's got it, the mail server sits in PN2.
> While diagnosing this, I connect to the server (using Putty) from a
> machine in PN1, using either a mail client or telnet I'm unable to make
> a connection to the mail server over port 25. Using tcpdump during this
> putty session I do not even see the SYN packets for the start of the
> connection from the machines in PN1. This is only when connecting to
> port 25. Obviously, I can connect to the server because I'm using
> putty. Also, I can see the SYN packets for the start of the connection
> when this same machine in PN1 attempts to connect to port 80. The
> problem seems to be when trying to connect over port 25. For some
> reason, the packets aren't being delivered to that address
> (188.8.131.52). This happens if I try to telnet to
> mail.whitneybaptist.org or telnet to 184.108.40.206 on port 25. The
> packets aren't being delivered. They're being sent somewhere else, or
> lost in digital purgatory.
> Now, from home (my home) let's call this PN3, I can send/receive mail
> using the church e-mail server. I, however, don't use CableOne. Are
> there routers that route traffic based on port number? It's almost as
> if traffic, that originates within the CableOne domain and travels
> through, but not outside, the CableOne domain, doesn't get routed to the
> correct address when it's destined for port 25.
So a common thread is that traffic on the ISP's net isn't going
out via yourserver.com:25 --- would seem to indicate port blocking,
which is quite common for port 25. Tried 587 or some weird alternate?
If the odds are a million to one against something
occurring, chances are 50-50 it will.
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