Thursday, August 18, 2011

Email Fundamentals: How to Send Email via Telnet

This is one of the essential troubleshooting tricks that an Exchange administrator needs to know, sending an email using Telnet from the command line.

Let’s say you’ve just configured a relay connector and want to test it from the server that you wish to allow relay from before you let that server’s owner know that it is all set up for them. Or perhaps you want to quickly test whether a another email server on the internet is accepting mail from your network.

For just about any scenario where you want to quickly test SMTP knowing this method is very useful.

Note: this technique requires the Telnet client to be installed on the computer you’re running the test from. For Windows XP and Windows Server 2003 it will already be installed, but Windows 7 and Windows Server 2008 need to install it first.

Installing the Telnet Client for Windows 7

To install the Telnet client on a Windows 7 computer use these steps.

  1. Open the Control Panel
  2. Click on Programs
  3. Click on Turns Windows Features on or off
  4. Scroll down the list until you see Telnet Client, and tick that box
  5. Click OK and close the Control Panel

Installing the Telnet Client for Windows Server 2008

To install the Telnet client on a Windows Server 2008 computer open a command prompt and run the following command.

C:\>servermanagercmd -i telnet-client
.........

Start Installation...
[Installation] Succeeded: [Telnet Client].

Success: Installation succeeded.

Installing the Telnet Client for Windows Server 2008 R2


To install the Telnet client on a Windows Server 2008 R2 computer open a PowerShell window and run the following command.

PS C:\> Import-Module servermanager
PS C:\> Add-WindowsFeature telnet-client

Success Restart Needed Exit Code Feature Result
------- -------------- --------- --------------
True No Success {Telnet Client}

Sending Email from the Command Line via Telnet


Open a command prompt and use Telnet to connect to the remote email server on port 25.

C:\>telnet esp-ho-ex2010a 25

If Telnet is able to connect to the remote server you should see its welcome banner.

220 ESP-HO-EX2010A.exchangeserverpro.net Microsoft ESMTP MAIL Service ready at T
ue, 9 Aug 2011 22:00:04 +1000

The first command to send is the HELO command. Some email servers will accept HELO on its own, others will require you to also provide a host or domain name along with it.

helo test.com
250 ESP-HO-EX2010A.exchangeserverpro.net Hello [10.0.1.11]

Next use the MAIL FROM command to tell the remote server who the email is from.

mail from: test@test.com
250 2.1.0 Sender OK

Now use the RCPT TO command to tell the remote server who to deliver the email to.

rcpt to: alan.reid@exchangeserverpro.net
250 2.1.5 Recipient OK

The final step for the bare minimum set of commands is the DATA command.

data
354 Start mail input; end with .

If you just want to send a blank message type a period “.” and press enter. Otherwise you can set a subject line for the message if you like. Use SUBJECT and then type your subject line, and press enter.

subject: this is a test message

Type any text you want to include with the message, press enter, and then finally type a period “.” and press enter to send the email.

sending a test message via telnet
.
250 2.6.0 [InternalId=320] Queued mail for delivery

If the message was queued for delivery then it has been accepted by the server. If this is an Exchange server that you control then you can use message tracking to troubleshoot further if the message doesn’t make it to the inbox that you were expecting.

Type the QUIT command to terminate the connection when you’re done.

SMTP Status Codes


You may notice along the way that after typing commands you see responses from the server starting with “250″.

250 is a good thing, and there are a lot of other SMTP status codes you’ll encounter the more you use this technique. For example an email server may deny your attempt to relay mail between two domains.

550 5.7.1 Unable to relay

Or you may encounter an email server that is explicitly blocking email from your domain.

554 5.1.0 Sender denied

There are a lot of different scenarios you might encounter here, and thankfully the SMTP status codes will help you troubleshoot them.

Now that you understand how to send email using Telnet and the command line I hope you find this technique very useful in the future.

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Set Multiple Sites as a Homepage in Internet Explorer 9

The Procedure for Setting the Homepage

First, open Internet Explorer 9 and then a tab for each site you want to set as a homepage. Browse to those websites.

Once you have all the websites loaded, click on the Tools button from the upper-right side of the Internet Explorer window. Then, click on Internet Options.

Internet Explorer 9

You set the homepage in the General tab. Simply click ’Use current’.

Internet Explorer 9

The websites you have loaded in each tab are now set as a homepage.Click OKand you are done.

Internet Explorer 9

From now on, when you start Internet Explorer 9, the websites which you set as homepages will be loaded in separate tabs.

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Sunday, August 7, 2011

Enabling And Disabling Services During Start Up In GNU/Linux

In any Linux distribution, some services are enabled to start at boot up by default. For example, on my machine, I have pcmcia, cron daemon, postfix mail transport agent ... just to name a few, which start during boot up. Usually, it is prudent to disable all services that are not needed as they are potential security risks and also they unnecessarily waste hardware resources. For example, my machine does not have any pcmcia cards so I can safely disable it. Same is the case with postfix which is also not used.

So how do you disable these services so that they are not started at boot time?

The answer to that depends on the type of Linux distribution you are using. True, many Linux distributions including Ubuntu bundle with them a GUI front end to accomplish the task which makes it easier to enable and disable the system services. But there is no standard GUI utility common across all Linux distributions. And this makes it worth while to learn how to enable and disable the services via the command line.

But one thing is common for all Linux distributions which is that all the start-up scripts are stored in the '/etc/init.d/' directory. So if you want to say, enable apache webserver in different run levels, then you should have a script related to the apache webserver in the /etc/init.d/ directory. It is usually created at the time of installing the software. And in my machine (which runs Ubuntu), it is named apache2. Where as in Red Hat, it is named httpd. Usually, the script will have the same name as the process or daemon.

Here I will explain different ways of enabling and disabling the system services.
1) Red Hat Method

Red Hat and Red Hat based Linux distributions make use of the script called chkconfig to enable and disable the system services running in Linux.

For example, to enable the apache webserver to start in certain run levels, you use the chkconfig script to enable it in the desired run levels as follows:

# chkconfig httpd --add
# chkconfig httpd on --level 2,3,5
This will enable the apache webserver to automatically start in the run levels 2, 3 and 5. You can check this by running the command:
# chkconfig --list httpd
One can also disable the service by using the off flag as shown below:
# chkconfig httpd off
# chkconfig httpd --del
Red Hat also has a useful script called service which can be used to start or stop any service. Taking the previous example, to start apache webserver, you execute the command:
# service httpd start
and to stop the service...
# service httpd stop
The options being start, stop and restart which are self explanatory.
2) Debian Method

Debian Linux has its own script to enable and disable services across runlevels. It is called update-rc.d. Going by the above example, you can enable apache webserver as follows:

# update-rc.d apache2 defaults

... this will enable the apache webserver to start in the default run levels of 2,3,4 and 5. Of course, you can do it explicitly by giving the run levels instead of the "defaults" keyword as follows:

# update-rc.d apache2 start 20 2 3 4 5 . stop 80 0 1 6 .

The above command modifies the sym-links in the respective /etc/rcX.d directories to start or stop the service in the destined runlevels. Here X stands for a value of 0 to 6 depending on the runlevel. One thing to note here is the dot (.) which is used to terminate the set which is important. Also 20 and 80 are the sequence codes which decides in what order of precedence the scripts in the /etc/init.d/ directory should be started or stopped.

And to disable the service in all the run levels, you execute the command:

# update-rc.d -f apache2 remove
Here -f option which stands for force is mandatory.

But if you want to enable the service only in runlevel 5, you do this instead:

# update-rc.d apache2  start 20 5 . stop 80 0 1 2 3 4 6 .
3) Gentoo Method

Gentoo also uses a script to enable or disable services during boot-up. The name of the script is rc-update . Gentoo has three default runlevels. Them being: boot, default and nonetwork. Suppose I want to add the apache webserver to start in the default runlevel, then I run the command:

# rc-update add apache2 default
... and to remove the webserver, it is as simple as :
# rc-update del apache2
To see all the running applications at your runlevel and their status, similar to what is achieved by chkconfig --list, you use the rc-status command.
# rc-status --all
4) The old fashioned way

I remember the first time I started using Linux, there were no such scripts to aid the user in enabling or disabling the services during start-up. You did it the old fashioned way which was creating or deleting symbolic links in the respective /etc/rcX.d/ directories. Here X in rcX.d is a number which stands for the runlevel. There can be two kinds of symbolic links in the /etc/rcX.d/ directories. One starts with the character 'S' followed by a number between 0 and 99 to denote the priority, followed by the name of the service you want to enable. The second kind of symlink has a name which starts with a 'K' followed by a number and then the name of the service you want to disable. So in any runlevel, at any given time, for each service, there should be only one symlink of the 'S' or 'K' variety but not both.

So taking the above example, suppose I want to enable apache webserver in the runlevel 5 but want to disable it in all other runlevels, I do the following:

First to enable the service for run level 5, I move into /etc/rc5.d/ directory and create a symlink to the apache service script residing in the /etc/init.d/ directory as follows:

# cd /etc/rc5.d/
# ln -s /etc/init.d/apache2 S20apache2

This creates a symbolic link in the /etc/rc5.d/ directory which the system interprets as - start (S) the apache service before all the services which have a priority number greater than 20.

If you do a long listing of the directory /etc/rc5.d in your system, you can find a lot of symlinks similar to the one below.

lrwxrwxrwx  1 root root 17 Mar 31 13:02 S20apache2 -> ../init.d/apache2

Now if I start a service, I will want to stop the service while rebooting or while moving to single user mode and so on. So in those run levels I have to create the symlinks starting with character 'K'. So going back to the apache2 service example, if I want to automatically stop the service when the system goes into runlevel 0, 1 or 6, I will have to create the symlinks as follows in the /etc/rc0.d, /etc/rc1.d/, /etc/rc6.d/ directories.

# ln -s /etc/init.d/apache2 K80apache2

One interesting aspect here is the priority. Lower the number, the higher is the priority. So since the starting priority of apache2 is 20 - that is apache starts way ahead of other services during startup, we give it a stopping priority of 80. There is no hard and fast rule for this but usually, you follow the formula as follows:

If you have 'N' as the priority number for starting a service, you use the number (100-N) for the stopping priority number and vice versa.

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