First of let me clear that all of the above steps are in addition to Qmail/Sendmail + Antispam(SpamAssassin) + Antivirus.
Let me explain each of the above point in some detail.
1. How razor works ?
Razor contains database of spam mails with signature, submitted manually by Email users. Every mail in your mailbox is checked against Razor's database, and if the mail found in database, marked as spam.
Razor can be used in two modes:
In Passive mode, you are just using database of Razor to reduce spam mails.
In Active mode, you are registering yourself with razor using razoradmin and submit spam mails to add them into Razor database.
2. What is catchall and "Reject" ?
For example, you are hosting mail service of xyz.com. A mail comes for a user called email@example.com
. Now, firstname.lastname@example.org
doesn't exist on xyz.com. While using Qmail, you are having three options for mails to email@example.com
a. Bounce message with subject - A bounce back message will be sent to "From" email id. This option is best for spammers.
Spammer send a mail from firstname.lastname@example.org
( non-existence account on yahoo ) to email@example.com
. Mail server of firstname.lastname@example.org
will send bounce back message to email@example.com
will send bounce back to firstname.lastname@example.org
. This way it will create a loop of mails, which stuck up mail queue on Mail server of xyz.com and slows down mail delievery.
b. Catchall email - All the mails to nonexist user for this domain will be delievered to this email-id. From above scenario just imagine how much mails user with catchall email address will receive.
c. Reject - Do not accept mail for nonexistence user. ( Best Option ) Mail server of xyz.com won't accept mail for nonexistence user for queueing.
Similar option may exist with Sendmail and other MTA.
3. Nothing more to say about PTR records. Some Mail Service provider check whether IP address corresponding to your mail sever is mapped back to some domain or not. If you are using hosting multiple sites on single IP, Add PTR record for any domain hosted on that IP.
4. "Sender Policy Framework (SPF) is an attempt to control forged e-mail. SPF is not directly about stopping spam – junk email. It is about giving domain owners a way to say which mail sources are legitimate for their domain and which ones aren't." MSN and some other Hosting provider checks SPF record for checking whether mail is generated from authenticated IP or not. You can generate SPF record for your domain form openspf.org.
Link : http://old.openspf.org/wizard.html?m...m&submit=Go%21
8. Now a days, most of the Mail Servers use SMTP authentication. But due to weak password, if any password of any mail id is cracked, a spammer can send thousands of mails using a simple script.
is redirected to email@example.com
. Any mail deilevered to firstname.lastname@example.org
will be delivered to email@example.com
. Consider a case when firstname.lastname@example.org
is catchall email address for the domain, all the spam mails will be forwardred to email@example.com
. But in case of redirected id, all the email addressed considered to be generated from xyz.com's mail server, which result in blacklisting of xyz.com's mail server.
I will post some email headers, in case of blacklisting by various Mail servers in next post.