Sending and Receiving EMail

Most of the time this is a painless task. You just set up your email client and hit the Send/Receive button and away you go. But what happens when things go wrong? How do you troubleshoot the problem? Our Knight in shining armour is telnet. You can use this program to manually perform the sequence of commands as shown below.

telnet mail.xxx.com 25

A typical conversation goes something like this (your entry in bold)

Sending Email

telnet mail.mydomain.com 25
220 mydomain.com ESMTP Sendmail 8.11.6/8.11.6; Thu, 26 Oct 2006 11:18:07 -0600
HELO fromme.com
250 mydomain.com Hello [xxx.xxx.xxx.xxx], pleased to meet you
MAIL FROM: test@
250 2.1.0 test@ Sender ok
RCPT TO: validuser@mydomain.com
250 2.1.5 validuser@mydomain.com… Recipient ok
DATA
354 Enter mail, end with “.” on a line by itself
Date: Sun,17 Aug 1997 18:48:15 +0200
From: Me <forged@dummy.com>
To: “You@Yours.com” <You@Yours.com>
Subject: This is a test message

This is the message body
.

250 2.0.0 k9QHLHX00862 Message accepted for delivery
QUIT
221 2.0.0 mydomain.com closing connection

Connection to host lost.

If your server supports ESMTP, it is also possible to start the conversation with EHLO instead of HELO. ESMTP allows for delivery status notifications and multiple attachment encodings

220 mydomain.com ESMTP Sendmail 8.11.6/8.11.6; Thu, 26 Oct 2006 16:11:25 -0600
EHLO fromme.com
250-mydomain.com Hello [xxx.xxx.xxx.xxx], pleased to meet you
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-SIZE
250-DSN
250-ONEX
250-ETRN
250-XUSR
250-AUTH PLAIN LOGIN
250 HELP

Receiving EMail

A typical POP3 (receiving) conversation is

telnet mail.mydomain.com 110
+OK AVG POP3 Proxy Server <9397.1161883939@mydomain.com> 7.1.400/7.1.408 [268.13.11/494]
USER validuser
+OK Password required for validuser
PASS xxxxxxxx
+OK validuser has 10 visible messages (0 hidden) in 1275592 octets.
STAT
+OK 10 1275592
LIST
+OK 10 visible messages (1275592 octets)
1 20018
2 19726
……..
9 18883
10 519
.
RETR 10
+OK 519 octets
Return-Path: <test>test@
Received: from fromme.com ([xxx.xxx.xxx.xxx])
by mydomain.com (8.11.6/8.11.6) with SMTP id k9QHLHX00862
for validuser@mydomain.com; Thu, 26 Oct 2006 11:21:48 -0600
Message-Id: <200610261721.k9QHLHX00862@mydomain.com>
X-Envelope-From: test@
X-Envelope-To: validuser@mydomain.com
X-Protocol: SMTP
Date: Sun,17 Aug 1997 18:48:15 +0200
From: Me <forged@dummy.com>
To: “You@yours.com” <You@Yours.com>
Subject: This is a test message
X-UIDL: O*5!!PS:”!7Jk”!~+=”!
X-Antivirus: AVG for E-mail 7.1.408 [268.13.11/494]
Mime-Version: 1.0
Content-Type: text/plain

This is the message body


No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.1.408 / Virus Database: 268.13.11/494 – Release Date: 24/10/2006

.
QUIT
+OK Pop server at mydomain.com signing off.

Connection to host lost.

You can see how easy it is for spammers to send fake or phishing emails – the only genuine piece of information in this header is my IP Address, which I have blanked out [xxx.xxx.xxx.xxx]

Other Tests

The other thing to do is to go to http://www.dnsstuff.com and fill out the DNS Lookup for the MX records of your domain in the top right box

Installing GnuPG-1.4.5

Step 1 – Download source

The first thing we need to do is download the source file from GnuPG.  I like to download the files directly to my server rather than downloading them to my PC and then uploading them to my server, so lets use a SSH session.  There are plenty of SSH Clients available, but PuTTY is available for free and does the job.  Instructions for configuring PuTTY for Westhost are available here.  Once you have logged in, create a directory to download your files to (for example, apps/dl) using the mkdir
[mylogin][~]$mkdir apps
[mylogin][~]$mkdir apps/dl

The files we need are only available via FTP from GnuPG.  If you clicked on the link to their site above, you will have found the latest version – at the time of writing this is 1.4.5.  Hover your mouse over the FTP link and you will find that the file we want to download is located at ftp://ftp.gnupg.org/gcrypt/gnupg/gnupg-1.4.5.tar.bz2, that is to say the file gnupg-1.4.5.tar.bz2 is located on the server called ftp.gnupg.org in the directory gcrypt/gnupg Follow the example below to download your own copy (user input is in bold).  It is good practice to download the signature file gnupg-1.4.5.tar.bz2.sig as well. 

If you prefer, you can download the gzipped file gnupg-1.4.5.tar.gz instead of gnupg-1.4.5.tar.bz.  You do not need both sets, although I download them in the example below.  GZip is just an older piece of software.  The command to extract the files would be gunzip instead of bunzip2

User Input System Output
cd apps/dl [mylogin][~/apps/dl]$
ftp ftp>
open ftp.gnupg.org Connected to ftp.gnupg.org.
220 Service ready for new user.
Name (ftp.gnupg.org:mylogin):
anonymous 331 Send e-mail address as password.
Password:
anon@ 230 User logged in, proceed.
Remote system type is UNIX.
ftp>
cd gcrypt/gnupg 250-The program GnuPG hosted here is a free software package
250-of the GNU Project, not a product of the GUUG e.V.  We call it
250-”Free Software” because you are free to copy and redistribute them,
250-following the rules stated in the license of the package.  For more
250-information, see http://www.gnu.org/philosophy/free-sw.html.
250-
250-If you are looking for service or support for GNU software, see
250-http://www.gnu.org/help/gethelp.html for suggestions of where to ask.
250-
250-If you would like to contribute to the development of one of these
250-packages, contact the package maintainer or the bug-reporting address
250-of the package (which should be listed in the package itself), or look
250-on www.gnu.org for more information on how to contribute.
250-
250-More information on GnuPG can be found at http://www.gnupg.org .
250-
250 Directory change successful.
ftp>
dir 200 Command okay.
150 About to send file list.
total 0
-rw-rw-r– 1 1000 1000 786 May 1 2003 README
-rw-rw-r– 1 1000 1000 796 Sep 24 2002 README~
-rw-rw-r– 1 1000 1000 107191 Sep 3 1999 gnupg-0.9.10-0.9.11.diff.gz
-rw-rw-r– 1 1000 1000 143753 Sep 7 1999 gnupg-0.9.11-1.0.0.diff.gz
…..
-rw-r–r– 1 1000 1000 118281 Aug 1 13:34 gnupg-1.4.4-1.4.5.diff.bz2
-rw-r–r– 1 1000 1000 3047120 Jun 25 15:22 gnupg-1.4.4.tar.bz2
-rw-r–r– 1 1000 1000 158 Jun 25 15:22 gnupg-1.4.4.tar.bz2.sig
-rw-r–r– 1 1000 1000 4272825 Jun 25 15:22 gnupg-1.4.4.tar.gz
-rw-r–r– 1 1000 1000 158 Jun 25 15:22 gnupg-1.4.4.tar.gz.sig
-rw-r–r– 1 1000 1000 3089617 Aug 1 13:34 gnupg-1.4.5.tar.bz2
-rw-r–r– 1 1000 1000 158 Aug 1 13:34 gnupg-1.4.5.tar.bz2.sig
-rw-r–r– 1 1000 1000 4348833 Aug 1 13:33 gnupg-1.4.5.tar.gz
-rw-r–r– 1 1000 1000 158 Aug 1 13:33 gnupg-1.4.5.tar.gz.sig
drwxrwsr-x 2 1000 1000 4096 Sep 24 2002 nls-updates
226 Transfer complete.
ftp>
type image 200 Command okay.
ftp>
passive Passive mode on.
ftp>
If you get the reply passive mode off, then type the command passive again.
get gnupg-1.4.5.tar.bz2 local: gnupg-1.4.5.tar.bz2 remote: gnupg-1.4.5.tar.bz2
227 Entering Passive Mode (217,69,76,44,163,131).
150 About to open data connection.
226 File transfer complete.
3089617 bytes received in 16.6 secs (1.8e+02 Kbytes/sec)
ftp>
get gnupg-1.4.5.tar.bz2.sig local: gnupg-1.4.5.tar.bz2.sig remote: gnupg-1.4.5.tar.bz2.sig
227 Entering Passive Mode (217,69,76,44,163,131).
150 About to open data connection.
226 File transfer complete.
158 bytes received in 0.0126 secs (12 Kbytes/sec)
ftp>
get gnupg-1.4.5.tar.gz local: gnupg-1.4.5.tar.gz remote: gnupg-1.4.5.tar.gz
227 Entering Passive Mode (217,69,76,44,161,185).
150 About to open data connection.
226 File transfer complete.
4348833 bytes received in 23.1 secs (1.8e+02 Kbytes/sec)
ftp>
get gnupg-1.4.5.tar.gz.sig local: gnupg.gz.sig remote: gnupg-1.4.5.tar.gz.sig
227 Entering Passive Mode (217,69,76,44,161,238).
150 About to open data connection.
226 File transfer complete.
158 bytes received in 3.3e-05 secs (4.7e+03 Kbytes/sec)
ftp>
!ls -l gnupg-1.4.5.tar* -rw-r–r– 1 mylogin myuser 3089617 Oct 30 04:45 gnupg-1.4.5.tar.bz2
-rw-r–r– 1 mylogin myuser 158 Oct 30 03:29 gnupg-1.4.5.tar.bz2.sig
-rw-r–r– 1 mylogin myuser 4348833 Oct 30 05:18 gnupg-1.4.5.tar.gz
-rw-r–r– 1 mylogin myuser 158 Oct 30 05:18 gnupg-1.4.5.tar.gz.sig
ftp>
dir gnupg-1.4.5.tar* 227 Entering Passive Mode (217,69,76,44,162,76).
150 About to send file list.
total 0
-rw-r–r– 1 1000 1000 3089617 Aug 1 13:34 gnupg-1.4.5.tar.bz2
-rw-r–r– 1 1000 1000 158 Aug 1 13:34 gnupg-1.4.5.tar.bz2.sig
-rw-r–r– 1 1000 1000 4348833 Aug 1 13:33 gnupg-1.4.5.tar.gz
-rw-r–r– 1 1000 1000 158 Aug 1 13:33 gnupg-1.4.5.tar.gz.sig
226 Transfer complete.
ftp>
quit 221 Service closing control connection.

Step 2 – Checking the download

Now that we have the source files on our server, we need to check that they have not been tampered with.  The simplest way is to issue the command bunzip2 -t gnupg-1.4.5.tar.bz2


[mylogin][~/apps/dl]$ bunzip2 -tv gnupg-1.4.5.tar.bz2
gnupg-1.4.5.tar.bz2: ok

However, this only checks that the archive is not corrupt.  You really need to check the file’s digital signature, but we don’t have any means to do that yet.  We can verify the checksum but GnuPG only publish the SHA1 checksum for the code and we do not have sha1sum installed on our server.  However, I can reveal ;) that the MD5sum is

811525965b4c0987e6418a7729a6444d gnupg-1.4.5.tar.bz2

If you save this text to the file gnupg-1.4.5.tar.bz2.md5, then enter md5sum -c gnupg-1.4.5.tar.bz2.md5 on the command line, you should get this response


[mylogin][~/apps/dl]$ md5sum -c gnupg-1.4.5.tar.bz2.md5
gnupg-1.4.5.tar.bz2: OK

If there was a problem with your download, you will get the following error message when testing the archive

bunzip2: gnupg-1.4.5.md5: data integrity (CRC) error in data

You can use the `bzip2recover’ program to attempt to recover
data from undamaged sections of corrupted files.

Step 3 – Other libraries

We need to download and install the libcurl, libiconv and gettext libraries before we can build GnuPG.  Also, since we do not have root access at Westhost, we need to tell all Linux packages to install to a different directory other than /usr/local.  We do this by specifying

./configure --prefix=/usr/mylocal
NOTE: Create the directory /usr/mylocal if it does not already exist

Library Command Download Location
libicurl wget http://curl.haxx.se/download/curl-7.16.0.tar.bz2
libicurl wget http://curl.haxx.se/download/curl-7.16.0.tar.bz2.asc
libiconv wget http://ftp.gnu.org/pub/gnu/libiconv/libiconv-1.11.tar.gz
libiconv wget http://ftp.gnu.org/pub/gnu/libiconv/libiconv-1.11.tar.gz.sig
gettext ftp ftp://mirrors.usc.edu/pub/gnu/gettext/gettext-0.16.tar.gz
gettext ftp ftp://mirrors.usc.edu/pub/gnu/gettext/gettext-0.16.tar.gz.sig

libiconv and gettext depend on each other, so we need to build libiconv then gettext and the rebuild libiconv.

Build libcurl

wget http://curl.haxx.se/download/curl-7.16.0.tar.bz2
wget http://curl.haxx.se/download/curl-7.16.0.tar.bz2.asc
bunzip2 -c curl-7.16.0.tar.bz2 | tar x
cd curl-7.16.0
./configure --prefix=/usr/mylocal
make
make install
cd ..

Build libiconv

wget http://ftp.gnu.org/pub/gnu/libiconv/libiconv-1.11.tar.gz
wget http://ftp.gnu.org/pub/gnu/libiconv/libiconv-1.11.tar.gz.sig
gunzip -c libiconv-1.11.tar.gz | tar x
cd libiconv-1.11
./configure --prefix=/usr/mylocal
make
make install
cd ..

Build gettext

ftp mirrors.usc.edu
 anonymous
 anon@
 cd pub/gnu/gettext
 mode image
 passive
 get gettext-0.16.tar.gz
 get gettext-0.16.tar.gz.sig
 quit
gunzip -c gettext-0.16.tar.gz |tar x
cd gettext-0.16
./configure --prefix=/usr/mylocal
make
make install

Rebuild libiconv

cd ../libiconv-1.11
make distclean
./configure --prefix=/usr/mylocal
make
make install
libtool --dry-run --finish /usr/mylocal/lib
libtool --finish /usr/mylocal/lib
cd ..

Step 4 – Creating the Executable

bunzip2 -c gnupg-1.4.5.tar.bz2 |tar x
cd gnupg-1.4.5
./configure --prefix=/usr/mylocal
make
make install

Once you have built GnuPG, you will need to create a few links as our directory is not in the PATH.

ln -s /usr/mylocal/bin/gpg /usr/local/bin/gpg

Alternatively, edit the PATH definition in /.bashrc to include /usr/mylocal/bin

You will also need to copy the configuration file
mkdir ~/.gnupg
cp -p /usr/mylocal/share/gnupg/options.skel ~/.gnupg/options