Troubleshooting Problems With Anti-Spam Systems
 Table of Contents
While I despise spam where irresponsible spammers send millions of e-mails,
I do think there is a place for responsible direct e-mail campaigns using
legitimate targeted opt-in lists where individuals have given permission
to receive information. Various anti-spam tactics are implemented nowadays
by ISPs to block spam, but they often harm innocent people and prevent
critical business e-mail from being delivered. I will try to explain what
methods are commonly used and how you can get around the problems they
are causing.
To cut down on the amount of spam e-mail that is sent, some ISPs are
blocking port 25 used to send e-mail from your computer. ISPs may block
connections from IP addresses that are on their black lists due to excessive
amount of spam sent from that addresses and may also perform a relay check
to prevent messages that are coming from open SMTP relays. Another popular
method to block spam is checking the sender's IP address against list
of dynamic IP addresses. If the IP address is dynamic, the e-mail is rejected.
About backup SMTP servers
The Professional
Edition of PostCast Server has a feature that allows you to specify
one or more backup SMTP servers. If only certain domains are unable to
receive messages from PostCast Server, you can use this option to forward
those messages to your ISP's or any third-party SMTP server. If PostCast
Server is unable to deliver a message, it can forward it to a backup SMTP
server. This enables the program to successfully send higher percentage
of messages, but unfortunately does not help if your ISP is blocking port
25. For more information, see the SMTP Gateways
topic.
Anti-Spam Methods:
- Overview
- Port
25 Blocking
- Internet Black and White Lists
- Blocking
Open Relays
- DNS
Lookups
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