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Re: sendmail on a laptop



On Wed, Dec 01, 2004 at 12:55:38AM -0400, Trevor Smith wrote:
> On December 1, 2004 12:37 am, Ernie McCracken wrote:
> > For awhile, I just used sendmail to deliver mail directly.  Then I found
> > that some of my mail was bouncing because ISPs had deemed my IP address
> > was part of a block of DHCP-assigned IP addresses.  This was presumably
> > done to keep spammers and virus-infected machines from sending mail
> > directly from their PC.
> 
> OK, this suggests a few questions to me:
> 
> 1. it appears you are saying that sending directly through my localhost's 
> sendmail *will* work from different networks. Was that what you found? (I 
> haven't tested yet.)

Yes, sendmail should work no matter what network it's on.  However, your
ISP or office network may have blocked outbound port 25.  I know it's
like that where I work.

In that case, it won't matter that sendmail works, because none of your
mail will get through due to firewall restrictions.

> 2. Assuming yes to #1 above, was it sending through sendmail that was causing 
> people to blacklist you? I don't quite understand the technology involved 
> well enough to see how this would be a problem.

No, it wasn't _me_ in particular that caused it.. at least, I hope not.
:-)

I think some (many?) ISPs simply blacklist a range of IP addresses that
are known to be dynamically assigned.  Their rationale being that email
coming directly from a machine with an IP address in that range can only
be caused by two things:

1. Spammer
2. Somebody's PC that is infected with a virus/trojan

I don't know if they still do this, but earthlink.net bounced all my
email with a little nastygram that said something to the effect of:
"This email came from a dynamically-assigned IP address.  Please use
your ISP's SMTP server."

So I ended up having to use my ISP's SMTP server, or I couldn't get
email to my parents because they happen to use earthlink. 



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