Re: smtp relay (whats it for)
- From: "N. Miller" <anonymous@xxxxxxxxxxxxxxxxx>
- Date: Sat, 30 Aug 2008 13:33:35 -0700
On Sat, 30 Aug 2008 10:59:02 +0100, rvj wrote:
Im trying to understand if SMTP relay is a solution looking for a problem
As I understand it, the protocol SMTP is needed to "talk" to the target mail
exchange
This is normally done via a SMTP relay server which accepts outgoing
requests from a number of clients and routes them onward
However as it is possible to buy Local SMTP relay on the client which will
send messages DIRECTLY to the target mail exchange
SMTP server is included in Windows XP Pro; not sure about which flavor of
Windows Vista would have it. Most flavors of Linux include SMTP servers, as
well. Or you can find free downloads online (I am running Mercury/32).
Can any one suggest reasons (url) why Local SMTP relay is not standard ?
Most ISPs prohibit end users from running servers in their AUP/TOS. It is
not easy to set up an SMTP relay secure from being an "open relay"; and you
most definitely do not want to run an open relay. Comcast, for one, will cut
off your access to outbound port 25 if you do; and other ISPs block outbound
port 25 from the get-go, making running an SMTP server moot.
It seems to avoid sending mail via third party servers and the associated
security pitfalls
At the expense of opening up new, maybe worse, security pitfalls for the end
user.
PS I guess the problem may be my understanding of DIRECTLY (client to
target mail exchange)
Most gateway (MX) mail servers block access from dynamically assigned IP
addresses (typical of residential Internet connections). Many U.S. providers
(most of the larger ones) block outbound port 25, so reaching a gateway (MX)
server becomes impossible, anyway.
Here is a result from trying to test the gateway (MX) mail servers of two of
the larger U.S. ISPs:
| 08/30/08 13:25:08 SMTP Verify User@xxxxxxx, at mailin-01.mx.aol.com
| Contacting 205.188.159.57
| 554- (RTR:BB) http://postmaster.info.aol.com/errors/554rtrbb.html
|
| HELO aosake.net
| 554 Connecting IP: 69.110.229.74
|
| Doesn't want to talk to us
| 08/30/08 13:25:25 SMTP Verify User@xxxxxxxxxxx, at mx1.comcast.net
| Contacting 76.96.62.116
| 554 IMTA18.westchester.pa.mail.comcast.net comcast 69.110.229.74 Comcast requires that all mail servers must have a PTR record with a valid Reverse DNS entry. Currently your mail server does not fill that requirement. For more information, refer to: http://www.comcast.net/help/faq/index.jsp?faq=SecurityMail_Policy18784
|
| HELO aosake.net
| Doesn't want to talk to us
Using a local SMTP relay agent would fail for both <%User_ID%@xxxxxxx> (and
related domains, 'aim.com', 'netscape.net'), as would email to
<%User_ID%@xxxxxxxxxxx>. And this is after I request a port 25 unblock from
"at&t Yahoo! HSI" (AT&T Worldnet DSL Service and AT&T FastAccess will not
unblock port 25).
I end up using my ISP's mail server as a "SmartHost", anyway. My local MTA,
Mercury/32, sends all outbound email through 'mail.pacbell.net'.
There are some benefits to running your own SMTP MTA, but you really need to
understand what is involved, as well as the security implications, and
AUP/TOS implications ("at&t Yahoo! HSI" is one of the few U.S. ISPs, and the
only *large* one, which does not explicitly prohibit servers. AFAIK, both
AT&T Worldnent DSL Service, and AT&T FastAccess have the same prohibition as
most other large U.S. ISPs, such as Comcast, Road Runner, and Verizon).
--
Norman
~Oh Lord, why have you come
~To Konnyu, with the Lion and the Drum
.
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- From: rvj
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