I work for a small business and outsourced our email hosting to Google. However, I noticed that spammers are using our From: First Last to send their spam messages. All bounced messages come to our catch only account. How do I stop this? How do I validate our domain using SPF? How do I configure a SPF for Google Apps domain using BIND 9 or djbdns?
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My users will only be checking mail, and I want to disable FTP access as well as shell access under CentOS Linux. How do I disable shell (SSH) and FTP access to a new or old user under Linux without deleting user account?
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Q. How do I verify input data such as email address under PHP programming language?
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I have CentOS Linux acting as a router for our small community-based college. I see logwatch and other cron job generating emails for the root account. How do I delete those emails? I don’t want to disable email facility but just wanted to get rid of all root emails. How do I delete root user mails (mailbox) file in Linux or Unix like system?
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Q. I’ve Postfix based CentOS Linux server. I need to blacklist email ID: user@abadboy.com . How do I blacklist email address with postfix? I also have spamassassin software installed.

A. By default, the Postfix SMTP server accepts any sender address. However you can block / blacklist sender email address easily with Postfix. It has SMTP server access table.

Open /etc/postfix/sender_access file
# cd /etc/postfix
# vi sender_access
Append sender email id as follows:
user@abadboy.com REJECT
Save and close the file. Use postmap command to create a database:
# postmap hash:sender_access
Now open main.cf and add code as follows:
smtpd_recipient_restrictions = check_sender_access hash:/etc/postfix/sender_access
Save and close the file. Restart / reload postfix MTA:
# /etc/init.d/postfix restart

You can also use spamassassin to blacklist email address. Just add to your own spamassassin configuration or to /etc/mail/spamassassin/local.cf file:
# vi /etc/mail/spamassassin/local.cf
Append blacklist as follows:
blacklist_from user@abadboy.com
Save and close the file. Restart spamassassin:
# /etc/init.d/spamassassin restart

spamassassin will marke mail as SPAM instead of rejecting the same.

Q. I would like to install latest and greatest Mozilla thunderbird mail client under Linux.

How do I download and install the same to read emails?

A. Mozilla’s Thunderbird 2 email application is more powerful than ever. Thunderbird 2 features many new enhancements to help you better manage your unruly inbox, and stay informed. Thunderbird 2 scales to the most sophisticated organizational needs while making it easy to find what you need. It is the best mail/news client with RSS and integrated spam filter support.

Download Thunderbird to your Linux desktop

=> Visit this site to download Thunderbird

Thunderbird 2.0 installation – Just untar file and install it

Let us say you would like to install thunderbird in your own home directory called /home/jerry/. Open X terminal and type following command.

Copy your downloaded file to /home/tom/ and untar it:
$ cp /home/tom/Desktop/thunderbird-2.0.0.0.tar.gz .
$ tar -zxvf thunderbird-2.0.0.0.tar.gz

Now software was installed. To start Thunderbird mail client, enter:
$ cd thunderbird
$ ./thunderbird

How do I install thunderbird for everyone?

Install thunderbird in /opt directory. Login as root user:
# cd /opt
# mkdir thunderbird
# cd thunderbird
# cp /home/tom/Desktop/thunderbird-2.0.0.0.tar.gz .
# tar -zxvf thunderbird-2.0.0.0.tar.gz

To start thunderbird, enter:
$ /opt/thunderbird/thunderbird &

How do I create thunderbird icon on my desktop?

Right click on your Linux desktop
Select Create Launcher
Fill the details as follows:

• Set name to : Thunderbird
• Set command to : /opt/thunderbird/thunderbird
• Set comment to : My Email Client
• Hit OK to create an ICON

A note about Ubuntu / Debian Linux user

If you are using Ubuntu / Debian Linux, open terminal and type the following command to install thunderbird:
$ sudo apt-get update
$ sudo apt-get install thunderbird