Quoting Paul M Foster <paulf@quillandmouse.com>:
> On Tue, May 04, 2010 at 03:45:13PM -0400, Paul M Foster wrote:
>
>> I feel silly asking this question, since I've been working with Linux
>> for over 15 years. But I've just never had to deal with the issue
>> before.
>>
>> Verizon FiOS (which I have) is, starting 8 June, going to block port 25
>> for customers who don't use Verizon's mail servers (which I don't).
>> Their alternate port is port 587. As I understand it, I'm supposed to
>> change my settings to this port, and all will be cosmic.
>>
>> Here's the thing, though. I tender mail to my local mailserver, which
>> connects to my internet mailhost via port 25. If I set my local
>> mailserver to connect via port 587, I can see how this would avoid
>> Verizon's port blocking. But my internet mailhost still wants to see a
>> connection on port 25. So does Verizon, when it sees a connection via
>> port 587 to an internet mailhost, then change the port to port 25 (which
>> is what my internet mailhost wants)?
>>
>> Can someone explain how this works?
>
> I seem to have answered my own question. When sending email via port
> 587, your internet mailhost must also accept mail on that port, or the
> whole thing won't work. In other words, if Verizon blocks port 25 and
> suggests instead port 587, your choices are: 1) get your mailhost to
> accept email connections on port 587, or 2) use Verizon's mail servers
> for your outbound mail. It's uncertain whether Verizon will accept email
> where the return address isn't on their mail server, however.
>
> Paul
>
I can almost bet that isn't going to work unless they only block
access based off src IP (since they know all their own IPs) but I am
sure they didn't do it this way.
Question: How do the other mail servers on the internet know to use
587 to deliver mail to your server? You are going to make me look at
what 587 is aren't you :)
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