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We'll look at what sniffing is and ways to avoid it.

I recently heard of a scenario where an individual was able to "sniff" or listen in to the wireless network traffic within range and from that, determine the account name, server and passwords from everyone who happened to check email while he was looking.

Scary huh?

And every time you use public internet facilities and hotspots, you may be at risk.

The simplest solution is to use webmail, making sure that it's on an "https", secure, connection. That's encrypted and safe from any sniffers that happen to see it.

But for many of us, that's not as optimal as we'd like. We'd like to keep using our regular email program and POP3/IMAP/SMTP servers.

Enter "SSH Tunneling".

"...every time you use public internet facilities and hotspots, you may be at risk."

Now, one of the requirements for SSH tunneling is that you have SSH (Secure SHell) access to your mail server. If you do not (and if you don't know, you probably don't), you can stop reading now. Check with your ISP if you like, to see if you can get it, but this technique relies on SSH being available on your server.

The good news is that once you have SSH access, there's no further server-side configuration.

In short, the technique works like this:

  • Using your SSH client or other tools, set up a "tunnel" for ports 25 and 110 on your machine to those same ports on your mail server. This does require that the client or tool be kept running.
  • configure your mail client to send to and fetch from "localhost" instead of your mail server.

That's really all there is to it.

Let's walk through the details for Windows users.

Start by grabbing the free SSH client and tools called PuTTY. Get the ZIP file that contains all the tools, because we'll be using more than just the PuTTY client.

One of the tools is called "plink". In a command shell, run the following:

plink -v -L 110:mailserver:110 -L 25:mailserver:25 -2 you@mailserver -N -pw yourpassword


  • -v: verbose - optional, but it will show you what plink is doing setting up the tunnel, and as long as the tunnel is active.
  • -L 110:mailserver:110: defines a tunnel of port 110 on your local machine to go to port 110 on the mailserver. Port 110 is the POP3 mail service. You would replace "mailserver" with the name of your POP server.
  • -L 25:mailserver:25: defines a tunnel of port 25 on your local machine to port 25 on the mailserver. Port 25 is the outgoing SMTP mail port. Again, you would replace "mailserver" with the name of your SMTP server.
  • -2: force ssh v2 protocol only. Optional, but slightly more secure. Use it unless your remote server doesn't support it.
  • you@mailserver: your ssh login account name @ your mailserver.
  • -N: no shell. Normally plink will also open up an interactive shell. For our purposes here we don't need one.
  • -pw yourpassword: your password for your ssh login account name. You can also leave this off to be prompted instead.

Leave plink running once it connects.

Now, in your email client (Outlook, Eudora, whatever), change both the POP3 and SMTP servers to "localhost".

You're done.

Here's what happens now: when you reload your email client, it will attempt to, for example, fetch POP3 mail from "localhost, port 110". Plink is listening to port 110 on your local machine, encrypts the data and sends it to the ssh server running on the mail server. There, the ssh server decrypts the data, and forwards it on to port 110 on the mail server. Data coming back is handled similarly, as is the SMTP port 25 conversation we defined as well.

A couple of additional notes...

You can tunnel other protocols (like mySql, imap, etc...) by adding "-L port:server:port" parameters to the plink line.

You can perform the port forwarding in PuTTY itself, the interactive client if you like - there is a section in the options for that, and it can be saved with the profile for that connection.

Remember that while your email is configured to use "localhost" as the mail server, the tunnel must be running (the plink command must be active). If it is not, email will fail.

There's technically nothing wrong with using this all the time. Still, what I've done in Outlook is to clone a separate profile that I can select at Outlook startup. So when I'm at home using my own secure network, the connections are direct and unencrypted as before. When traveling, I start the tunnel, and select the profile that uses it.

Other SSH clients do support tunneling though not all. PuTTY is free, and works well for me.

Article C2341 - April 25, 2005 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

Justin B.
May 23, 2005 7:41 AM


Do the servers involved have to be configured to support the tunnel? How standard is this for SMTP and POP3 servers to support SSH tunnels?

I have tried plink (as described above) at my place of business and received errors as follows:
Network error: Connection refused
FATAL ERROR: Network error: Connection refused

I'm fairly certain that I've followed your instructions properly which leads me to believe that our servers do not support SSH tunneling.

Thanks for the article!

May 23, 2005 7:56 AM

It definitely requires server-side support, and it sounds like your ISP doesn't have it. SSH is completely separate from SMTP and POP3 ... it's a remote terminal protocol that can also be used to tunnel other protocols. You'll have to check with your ISP.

Justin B.
May 23, 2005 8:36 AM

My applogies, you did answer my questions above. As the advertisement was inserted in front of it, I didn't see there was usable information on to the right of the ads.


September 7, 2005 6:47 AM

You can sniff HTTPs traffic on the wireless. All the person has to do is get your computer to accpet thier certificate rather than the real host's. There are several ways of doing this.

Proff of concept:

Antonio Ribeiro
November 16, 2005 3:57 AM

Hi Leo,
Sometimes, when I am at my work I use my laptop to check my email connecting through a wireless network in range.
I have in my laptop a free version of ZoneAlarm security software (basic firewall protection). It says that my computer is hidden and protected from hackers and that sharing is not allowed.
Do you think that it is enough to keep my computer safe when I am online and checking my email?
Do I still need set up this "complicated" process of tunneling to be secure?

Leo A. Notenboom
November 16, 2005 9:53 AM

Having a firewall does NOT protect the data that leaves your computer. Any internet surfing you do, or email you read, can potentially be viewed by someone else nearby without your knowledge, unless you take steps, like encrypting the data.

November 21, 2005 12:41 AM

How about using sites like

November 22, 2005 9:01 PM

No guarantees, of course, but it definitely looks like proxyweb is routing your conversations over a secure connection.

March 24, 2006 11:24 PM

hi i m omair my id has been hacked my id old password is immobhaijan and old secret answer is sanoberjan plz my new passwor and new secret answer mail me my id

michelle guy
April 24, 2006 5:11 AM

A while ago i used msn to have a chat, someone entered my msn chat from oct 05 and then forwarded it to me, how could they do this when i havent saved the conversations??THANK YOU

April 24, 2006 10:16 AM

Remember it takes two people to chat. Either of them can save the conversation in MSN Instant Messenger. If you didn't, then perhaps the person you were chatting with did.

Ruth Stevens
June 11, 2006 5:42 AM

Hi, Leo. Do you know of any stats, or have a sense, of how widespread it is for websites to sniff and use the email addresses of consumers who visit the site?

June 11, 2006 2:30 PM

Pretty close to zero. A website cannot "sniff" your email.

Now, if spyware were installed, that could allow anyone (website or not) to sniff. So make sure your spyware scanners are up to date:

And if you put yoru email address in a public place, like posting in the body of a comment on a site like this, then there are spiders that scan websites looking for things that look like email addresses, and hence could harvest your email address that way. This article has more:

June 13, 2006 9:59 AM


I sometimes check my email at work on a company computer,I am not sure if spyware was installed, but i do know there is a firewall. My question is, can management read my personal emails with the use of spyware? Also, is there anyway to safe guard hotmail, to prevent snoopers?


Leo A. Notenboom
June 13, 2006 3:54 PM

Of course your company can be sniffing. AND it's legal. They own all the peices that connect you to the internet, and could install sniffing software or hardware anywhere along the way.

etienne DeLigenza
August 11, 2006 8:22 AM

I have a mac account how easily can it be looked at?

najir pandey
December 1, 2006 2:53 PM

how do i protect my computer from being sniffed from msn monitor and sniffer? if u can.. pls tell me in simple words.

February 3, 2007 5:07 PM

can i keep my msn

February 7, 2007 8:17 PM

hey i dont wanna my brother ro look at my emails kk that

August 19, 2007 10:06 AM

can my ex find out that i was snooping? I logged on to hotmail as him - but the guilt hit straight away and so i logged out almost immediately. Can he tell that i logged on to his email from somewhere else? (we live at opposite ends of the world). I didn't open any of his emails or anything.

May 11, 2008 1:16 PM

i do not want any one 2read my email accoun. so how can i stop that help me please.

thank u

June 16, 2008 7:36 AM

Hello Leo; I was wondering if it is possible to use SSH access (Putty or other SSH client) with free email servers such as Gmail or yahoo? I mean, Does any free email service providers allows users to connect to their email servers via SSH? ... I have been doing some research and it looks that none of the free email providers worldwide supports and allows users to connect to their email servers using SSH. Does anyone knows about a free email service provider which allows users to connect via SSH? I mean, for Free.

June 17, 2008 4:13 PM

Hash: SHA1

I'm not aware of any free services that allow for SSH

With *some* you can do secure SMTP and POP3 instead - that's
typically easier to set up anyway. Check with the provider.


Version: GnuPG v1.4.7 (MingW32)


July 29, 2008 2:36 PM

I believe someone hacked into my yahoo e-mail account and took some e-mails and forwarded them to someone else. Just not sure how this can happen?

Betty Ledesma
September 20, 2008 11:08 AM

I have Yahoo as E mail. I can tell someone is spying on my E mails and some get deleted before I can see them I have windows visa and want to use my windows mail but don't know how to set it up. I also have Verizon as broadband built into my computer which I purchased from Dell. I don't feel secure at all, when I go into my acct, my computer makes me shut down without signing off. I really need security. PLEASE HELP. I have macAfee but it seems like I am getting phising pages instead of the real thin.

September 20, 2008 11:10 AM

Want is the best secure e-mail to use. I use yahoo because it is free. What do you suggest?

December 16, 2008 7:49 PM

Or anyone else that knows the answer. Would a proprietary email program such as the original Juno 5 be safer than Windows mail? I am not sure if its POP or not, but I do not think it is.


March 18, 2009 10:01 AM

If I scan all my important docs - birth certificates, credit cards info, etc and email it to myself to keep in a file that can be accessed by myself anywhere I am - Is it safe, can anyone else access the info in my hotmail account?


Given the frequency with which I hear about account theft and hacks, there's no way anyone should be keeping that kind of information in a free email account like Hotmail.

Even mailing it to yourself is dangerous, because the mail travels unencrypted, and could be sniffed somewhere along the way.

Don't do it.
- Leo

December 15, 2009 12:13 PM

Someone has seen my email, they have also seen emails sent 2 me.I have a lap top, just wanted 2 know if emailed pictures get saved 2 the computer. Cant figure out how they were able to see pictures that were only through emails. help

January 11, 2011 8:19 PM

I was just wondering if you can tell me how dating sites get your information because they keep sending me things that I do not want and my boyfriend thinks thigs are going on that are not. Please Help!!!!!

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