Here are some articles about Message Submission Program (MSP):

• http://www.sendmail.org/m4/msp.html
• http://www.ilkda.com/sendmail/MSP.htm
• http://www.sendmail.org/m4/features.html
• http://www.aripollak.com/qmailmsp/
• http://www.fehcom.de/qmail/smtpauth.html
• http://www.fehcom.de/qmail/spamcontrol/README_spamcontrol.html

Here are some resources for Qmail:

• QmailToaster 
• inter7. inter7 and QmailToaster are two related websites that provide email softwares and packages for Qmail. Worth to check out.
• Qmailrock is another resource for qmail.
• NRG4 is commonly used ISP's qmail-ldap

Here are some posts related to Zimbra mail server's ports and configuration:

Prepare the VPS

Before we install Zimbra, we must install the follow packages

root@HN# vzctl exec 101 yum install ant sysstat gmp compat-libstdc++-296 compat-libstdc++-33

The above list should be good enough for Zimbra 6. If installing Zimbra 5, then we also have to have:

The following are a serie on "Virtual Users And Domains With Postfix, Courier And MySQL (CentOS 5.1)" in howtoforge:

There are a number of tools out there that helps you to test if a domain has been blacklisted. There is a good one:

http://www.blacklistalert.org/

 Reference http://www.imminentweb.com/technologies/implement-domainkeys-identified-...

• an email
• http://www.ijs.si/software/amavisd/amavisd-new-docs.html#dkim

If you want to enable cdb support for Postfix on Gentoo, "USE=cdb emerge -v postfix" will always pull in cdb, instead of tinycdb.

Another thing to note is that tinycdb conflicts with cdb.

In order to use tinycdb in place of cdb, you can first emerge tinycdb. This will unmerge cdb for you. So, if you had cdb installed, you must find out whether you have the green light for tinycdb. Run "equery d dev-db/cdb" to check for dependencies.

Install and configure DCC

The current stable version for DCC in Portage is 1.3.55. That's a bit too old. You can check so by doing "emerge -pv dcc".

To get the latst DCC software, goto http://www.rhyolite.com/dcc/, and then read http://www.rhyolite.com/dcc/INSTALL.html.

Now follow My other article Setup DCC to Use Remote Public Servers.

authdaemond

You can change the number of authdaemond processes in the file /etc/courier/authlib/authdaemonrc:

daemons=2

This line sets the number of authdaemond processes to 2.

saslauthd

To change the number of saslauthd processes, edit the file /etc/conf.d/saslauthd (in Gentoo):