[CentOS] Sendmail problem

Wed Apr 12 11:27:58 UTC 2006
Johnny Hughes <mailing-lists at hughesjr.com>

On Wed, 2006-04-12 at 07:13 -0400, Thomas E Dukes wrote:
>  
> > -----Original Message-----
> > From: centos-bounces at centos.org 
> > [mailto:centos-bounces at centos.org] On Behalf Of Alexander Dalloz
> > Sent: Wednesday, April 12, 2006 7:06 AM
> > To: CentOS mailing list
> > Subject: RE: [CentOS] Sendmail problem
> > 
> > Am Mi, den 12.04.2006 schrieb Thomas E Dukes um 2:23:
> > 
> > > Here'sanother bounce email:
> > > 
> > > The original message was received at Tue, 11 Apr 2006 
> > 19:16:44 -0400 
> > > from localhost.localdomain [127.0.0.1]
> > > 
> > >    ----- The following addresses had permanent fatal errors ----- 
> > > <xxxxxx at comcast.net>
> > >     (reason: 521-EHLO/HELO from sender 71.31.91.127 does not map to 
> > > localhost.localdomain in DNS)
> > > 
> > >    ----- Transcript of session follows ----- ... while talking to
> > > gateway-s.comcast.net.:
> > > >>> MAIL From:<apache at localhost.localdomain> SIZE=2176
> > > <<< 521-EHLO/HELO from sender 71.31.91.127 does not map to 
> > > localhost.localdomain in DNS <<< 521-sending machine name must be 
> > > provided as a fully <<< 521-qualified domain via EHLO/HELO command.
> > > <<< 521-see section 4.1.1.1 and 4.1.4 of RFC 2821 <<< 521 
> > 521: Comcast 
> > > requires that all mail servers must have a PTR record with a valid 
> > > Reverse DNS entry. Currently your mailserver does not fill that 
> > > requirement. For more information, refer to:
> > > http://www.comcast.net/help/faq/index.jsp?faq=Email118405
> > > 554 5.0.0 Service unavailable
> > 
> > 2 things:
> > 
> > 1) Your mail host at that time of the mail had the hostname 
> > localhost.localdomain, thus your Sendmail used it for 
> > EHLO/HELO. You fixed that meanwhile
> > 
> > 2) The remote side requires not only a valid forward DNS 
> > record (palmettodomains.com points to that IP) but too a 
> > matching reverse one.
> > From here I can't judge whether the named IP is static and 
> > thus assigned by your ISP. If that is the case then you 
> > really should take care for both types of DNS entries. If not 
> > (you are on an dynamic line) you should use your ISP's mail 
> > host as SMART_HOST within your Sendmail configuration. DynDNS 
> > is a very bad base for reliable mail services.
> > 
> > Alexander
> 
> Hello Alexander,
> 
> Yes, I have a dynamic IP address.  If I use my ISPs mail host as the
> SMART_HOST, would that cause relaying problems?  I tried that on the mail
> client end a while back and got errors about relaying.
> 
> Thanks, I'll give it a try.

Just as a side note here ... the majority of mail servers now use a
technique called Realtime Blackhole List (RBL).

Many of the new lists contain the IPs of all dynamic Cable/DSL providers
as a huge amount of spam is sent via broadband PC's that have been
compromised.

It is a losing proposition to use dynamic machines to send reliable e-
mail as a server ... at least that has been my experience.
 
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