ISPs blocking SMTP connections from dynamic IP address space

[Lucas Holt]

Just make sure they are truly dynamic ips.  Many people block ips identified
as "DSL" connections.  Those are not necessarily dynamic ip based.  My mail
server runs on a business package dsl with 5 static ips.  Not everyone can
afford T1/T3 connections.  As for getting a "real mail server", that would
involve colo or getting a T1.  My dsl package is only ~$50 a month.  Much
cheaper than colo and I can get physical access to the box whenever I want.
SBC allocates separate class C's for dedicated customers.  I'm sure its
possible to distingish the two.

As for the 550: Spammer message, that is definetely on the other end.  Some
anti-spam add-ons for mail servers automatically reject mail like this.  In
addition, admins often block specific domains or ip addresses manually in
their config files.  I have about 15 ips and domains in my sendmail config
file because of repeat offenders who send spam or viruses.