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Adding DNSBL to Postfix can be a great advantage as these services will help you defend against email spam. What these services does, is to provide a realtime database over IP addresses that are sending spam. If Postfix gets a positive result looking at a certain IP address, it will reject that mail.

Installation

OS: Ubuntu/Debian

Installation is simple, you just need to edit the main.cf file of Postfix.

nano /etc/postfix/main.cf

Edit the line starting with

smtpd_recipient_restrictions = ...

In the end of that line before “permit” insert content like this

, reject_rbl_client cbl.abuseat.org, reject_rbl_client bl.spamcop.net, reject_rbl_client zen.spamhaus.org

Reload Postfix to load the new rules

/etc/init.d/postfix reload

You can specify as many DNSBL servers you like.

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Running a virtual host invironment might from time to time require different configurations for each host. Recently i was asked to disallow the POST method while whitelisting the method for a few IP numbers – someone must have abused some kind of formular on the homepage.

The limitation was achieved in the following way.

Inside the tags of:

<VirtualHost *:80>
 ...
</VirtualHost>

You should place the following code.

RewriteEngine on
RewriteCond %{THE_REQUEST} ^(POST)\ /.*\ HTTP/\d\.\d$
RewriteCond %{REMOTE_ADDR} !(x.x.x.x|y.y.y.y)
RewriteRule .* - [F]

Then restart Apache and the configuration will be loaded.

Explanations

  • Line 2: You can specify several methods inside the parentheses seperated by a pipe (|). For instance (POST|HEAD)
  • Line 3: Insert the desired IP adresses to be whitelisted, again seperated by a pipe (|).

NOTE

You will have to have the Apache rewrite module installed and enabled.

Available methods can be found under Apache docs.

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These steps can be used in order to migrate content of a Courier IMAP account into a Dovecot IMAP account. Have in mind if you are using these steps for POP3, that all emails from the server will be re-downloaded (in case you are leaving a copy on the server) causing a lot of duplicates in your email client.

Prerequisities: Obtain a copy of your courier content on the dovecot server preferably in /var/tmp/

Enter the Dovecot Maildir folder and empty it

cd /var/vmail/[domain.com]/[user]/Maildir/
rm -rf ./* ./.*

Copy your Courier mailbox content

cp -R /var/tmp/[user]/. .

Search and replace the content of courierimapsubscribed and rename/copy it

sed -i 's/\(INBOX.\|INBOX\)//g' courierimapsubscribed
sed -i '/^$/d' courierimapsubscribed
cp courierimapsubscribed subscriptions

Rename courierimapuiddb

mv courierimapuiddb dovecot-uidlist

Change ownership of the whole into vmail

chown -R vmail:vmail ./* ./.*

That’s it! Now go browse your content from webmail or your favorite email client.