[TriLUG] OT: ATT UVerse internet access

matt at noway2.thruhere.net matt at noway2.thruhere.net
Thu Mar 31 14:47:04 EDT 2011


> On 3/31/11 2:23 PM, Chris Merrill wrote:
>> On 3/30/2011 3:29 PM, bak wrote:
>>> I got around this by using the 'submission' port. Modern UNIX MTAs have
>>> this turned on by default. It is basically just
>>> SMTP-with-authentication-by-default; no relaying. The well-known port
>>> is
>>> 587. See RFC2476.
>>
>> I was not aware of this port.  But I'm a little confused about the "no
>> relaying"
>> part.  If I am using it to send email to our customers, is that not
>> relaying?
>> If not, then I don't understand the distinction. I thought contacting an
>> SMTP
>> server to send e-mail to a user on some other server IS relaying ???
>
> I think my brain was looking at it from a server rather than a user
> perspective when I wrote that.
>
> An MTA's regular SMTP port will do two things:
>
> -- Allow anyone[1] to relay a message into it, unauthenticated, as long
> as it understands that it is responsible for mail for that domain/address
>
> -- Allow an authorized group of people, after being authenticated, to
> submit a message that will be forwarded to any address
>
> The submission port is meant do the second thing, but not the first.
>
> Sorry to be imprecise :)
>
> [1] Usually after being subjected to various anti-spam measures like a
> blackhole list, header checks, reverse name lookup, size limitations...
>
I am still fuzzy on this one....

If port 25 is blocked, wouldn't you still have a problem sending mail out
or would you have to relay through your ISP's SMTP server?

And what about incoming messages, wouldn't they still attempt to com in on
port 25 and wouldn't a lack of connection just be treated as if your MTA
was down?

I understand that >99% of the populace doesn't run a mail server and that
when they do inject mail directly it is almost guaranteed to be spam, but
I have a problem with the whole mechanism vs policy thing of blocking
ports.

At least it was possible to get the block removed.





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