On Wed, Mar 31, 2004 at 03:39:08PM -0500, Reuben D. Budiardja wrote: > > Sorry if this is a little bit OT, but I know some people is knowledgeable > about this. Guilty :-) > But when I check the originating IP of this user (he uses his own ISP) here: > http://www.dnsbl.us.sorbs.net/cgi-bin/lookup?js&IP= > > I found entry in the "Dynamic IP Space " section. Looks like his ISP, or even > his IP block is in the list of SORBS. > And this > http://mail-abuse.org/cgi-bin/lookup > > shows his originating IP in the DUL list (whatever that is). DUL = Dialup User List Basically what is happening is that the SMTP server is using a dynamically assigned IP address. Every SMTP server has the option of checking the list of dynamically assigned addresses to accept or deny that particular transaction. Many major ISPs now check this list for incoming e-mail. They also notify the collectors of changes in this address space. Naturally, they will check this for incoming e-mail, but not originating e-mail which they expect to come from their own subscribers with dynamic addresses. By checking this list, you have the potentially to block a *LOT* of spam. Infected systems on a cable modem have been measured to send 1 million or more e-mails per day. Personally, I have an SMTP server running and I block e-mail from dynamic addresses even though I'm on a dynamic address myself. The workaround for the end user is to forward all e-mail to the ISP. In sendmail, that's known as a smart host, like this: # grep [ewilts@p6000 ewilts]$ grep -i smart /etc/mail/sendmail.mc define(`SMART_HOST',`smtp:smtp.comcast.net')dnl smtp.comcast.net does nice things like throttle large amounts of e-mail. It normally has absolutely no impact unless I blast stuff out to a mailing list, in which case it slows the e-mails down by blocking new e-mails from me for a while and then accepting them again. sendmail handles that transparently. The advantage to me is I feel a bit more protected about people using comcast to blast spam out. I wouldn't feel offended at all if comcast blocked me getting out directly via port 25 and forced us all comcast users to use their mail servers. Every little bit ISPs can do to reduce spam woud help. -- Ed Wilts, Mounds View, MN, USA mailto:ewilts@xxxxxxxxxx Member #1, Red Hat Community Ambassador Program -- redhat-list mailing list unsubscribe mailto:redhat-list-request@xxxxxxxxxx?subject=unsubscribe https://www.redhat.com/mailman/listinfo/redhat-list
