SMTP, testing via Telnet - Revision history

77.104.39.59: /* LOGIN method */

2013-02-12T14:47:18Z

Wojtekl: /* PLAIN method */

2012-07-07T14:17:40Z

PLAIN method

Wojtekl: /* PLAIN method */

2012-07-07T13:03:14Z

PLAIN method

Wojtekl: /* PLAIN method */

2012-07-07T13:02:23Z

PLAIN method

Wojtekl at 11:30, 7 July 2012

2012-07-07T11:30:51Z

Jimbo at 14:19, 13 September 2010

2010-09-13T14:19:13Z

Jimbo at 19:04, 29 December 2008

2008-12-29T19:04:00Z

Jimbo: /* See Also */

2008-12-29T18:49:20Z

66.83.151.234 at 18:45, 29 December 2008

2008-12-29T18:45:14Z

New page

When troubleshooting problems with SMTP service - your own, or others - it is frequently very helpful to be able to "speak" to the SMTP server directly, rather than going through a mail client which won't necessarily tell you exactly what the SMTP server is saying. You can easily do this with the '''telnet''' client.

Note that many ISPs do not allow outbound connections on port 25 to any SMTP server but their own - if you get timeouts when trying to connect to port 25, you should try port 587, which is the standard ESMTP port. (Port 587 connections normally require SMTP AUTH, which is covered below.)

==Testing an SMTP service via telnet==

ph34r# '''telnet localhost 25'''
Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
220 ESMTP
'''HELO justtesting'''
250
'''MAIL FROM: me@telnettingin.com'''
250 ok
'''RCPT TO: postmaster@mail.getsdeliveredhere.net'''
250 ok
'''DATA'''
354 go ahead
'''To: postmaster@mail.getsdeliveredhere.net'''
'''From: telnetclient@mail.getsdeliveredhere.net'''
'''Subject: this is a test message'''
'''Date: Thu, 21 Jun 2007 11:11:40 -0400'''
'''Just testing SMTP functionality by telnetting in to port 25. I'll end this message now'''
'''by entering in a line with nothing but a period in it and hitting return.'''
'''.'''
250 ok 1103093638 qp 87827
'''QUIT'''
221
Connection closed by foreign host.

Okay - our [[SMTP]] server just accepted a telnet connection, responded like a mailserver, and accepted a nice little test email for delivery. (Any response other than a '''250 ok''' would represent an error of one sort or another.)

==Testing SMTP AUTH via telnet==

===PLAIN method===

First, we need to generate a base64-encoded string for the PLAIN method, in the form of [null]username[null]password :

# '''perl -MMIME::Base64 -e 'print encode_base64("\0user\@domain.com\0password");' '''
AHVzZXJAZG9tYWluLmNvbQBwYXNzd29yZA==

'''IMPORTANT NOTE:''' notice that we escaped the '@' character with a backslash! If you don't, Perl will try to evaluate it as an array, and while you won't get an error, you won't get a usable hash, either.

OK, let's telnet in:

ph34r# '''telnet localhost 25'''
Trying 127.0.0.1...
Connected to localhost.privatedns.com.
Escape character is '^]'.
220 mail.server.local ESMTP

Great, we got a banner. OK, now let's tell it we want to use extended SMTP with the "ehlo" command:

'''ehlo test'''
250-mail.server.local
250-AUTH LOGIN PLAIN
250-AUTH LOGIN PLAIN
250-STARTTLS
250-PIPELINING
250 8BITMIME

Alright. Good. Notice that we support two AUTH methods: LOGIN, and PLAIN. We'll issue an AUTH PLAIN command, using the string we generated for it above:

'''AUTH PLAIN AHVzZXJAZG9tYWluLmNvbQBwYXNzd29yZA=='''
235 ok, go ahead (#2.0.0)

Excellent! Our authentication proceeded just fine. If we would like, we can now send a message just as we would have in the regular SMTP session listed above; or we can simply '''quit''' now if all we wanted to test was the authentication itself.

===LOGIN method===

If we want to try the LOGIN method, we'll need to generate separate base64-encoded strings for the username and the password:

ph34r# '''perl -MMIME::Base64 -e 'print encode_base64("user\@domain.com");' '''
dXNlckBkb21haW4uY29t
ph34r# '''perl -MMIME::Base64 -e 'print encode_base64("password");' '''
cGFzc3dvcmQ=

Now we telnet back in, '''ehlo''' as before, and this time authenticate using the LOGIN method:

'''AUTH LOGIN'''
334 VXNlcm5hbWU6
'''dXNlckBkb21haW4uY29t'''
334 UGFzc3dvcmQ6
'''cGFzc3dvcmQ='''
235 2.0.0 Authentication successful

Again, excellent. (If you were curious, the 334 and 235 SMTP messages are also Base64 encoded, and decode to "Username:" and "Password:".) You can either send a test message with the same commands as in the plain SMTP example at the top, or you can simply '''quit''' if you just wanted to test the authentication.

==See Also==
[[Daemons, testing via Telnet]]
[[IMAP, testing via Telnet]]
[[POP3, testing via Telnet]]

[[Category:FreeBSD for Servers]] [[Category:Common Tasks]]

@@ Line 46: / Line 46: @@
 '''IMPORTANT NOTE:''' notice that we escaped the '@' character with a backslash!  If you don't, Perl will try to evaluate it as an array, and while you won't get an error, you won't get a usable hash, either.
-'''NOTE:''' you can also use online encoding [http://www.motobit.com/util/base64-decoder-encoder.asp] though it's not very safe.
+'''NOTE:''' you can also use online encoding e.g. [http://www.motobit.com/util/base64-decoder-encoder.asp] though it's not very safe.
 OK, let's telnet in:

@@ Line 46: / Line 46: @@
 '''IMPORTANT NOTE:''' notice that we escaped the '@' character with a backslash!  If you don't, Perl will try to evaluate it as an array, and while you won't get an error, you won't get a usable hash, either.
-'''NOTE:''' you can also use online encoding [http://www.motobit.com/util/base64-decoder-encoder.asp]though it's not very safe.
+'''NOTE:''' you can also use online encoding [http://www.motobit.com/util/base64-decoder-encoder.asp] though it's not very safe.
 OK, let's telnet in:

← Older revision		Revision as of 11:30, 7 July 2012
Line 45:		Line 45:

	'''IMPORTANT NOTE:''' notice that we escaped the '@' character with a backslash! If you don't, Perl will try to evaluate it as an array, and while you won't get an error, you won't get a usable hash, either.		'''IMPORTANT NOTE:''' notice that we escaped the '@' character with a backslash! If you don't, Perl will try to evaluate it as an array, and while you won't get an error, you won't get a usable hash, either.
		+
		+	'''NOTE:''' you can also use online encoding [http://www.motobit.com/util/base64-decoder-encoder.asp]

	OK, let's telnet in:		OK, let's telnet in:

← Older revision		Revision as of 19:04, 29 December 2008
Line 1:		Line 1:
−	When troubleshooting problems with SMTP service - your own, or others - it is frequently very helpful to be able to "speak" to the SMTP server directly, rather than going through a mail client which won't necessarily tell you exactly what the SMTP server is saying. You can easily do this with the ~~'''~~telnet~~'''~~ client.	+	When troubleshooting problems with SMTP service - your own, or others - it is frequently very helpful to be able to "speak" to the SMTP server directly, rather than going through a mail client which won't necessarily tell you exactly what the SMTP server is saying. You can easily do this with the [[telnet]] client.

	Note that many ISPs do not allow outbound connections on port 25 to any SMTP server but their own - if you get timeouts when trying to connect to port 25, you should try port 587, which is the standard ESMTP port. (Port 587 connections normally require SMTP AUTH, which is covered below.)		Note that many ISPs do not allow outbound connections on port 25 to any SMTP server but their own - if you get timeouts when trying to connect to port 25, you should try port 587, which is the standard ESMTP port. (Port 587 connections normally require SMTP AUTH, which is covered below.)

@@ Line 91: / Line 91: @@
 2.0.0 Authentication successful
-Again, excellent.  (If you were curious, the 334 and 235 SMTP messages are also Base64 encoded, and decode to "Username:" and "Password:".)  You can either send a test message with the same commands as in the plain SMTP example at the top, or you can simply '''quit''' if you just wanted to test the authentication.
+Again, excellent.  (If you were curious, the 334 SMTP messages are also Base64 encoded, and decode to "Username:" and "Password:".)  You can either send a test message with the same commands as in the plain SMTP example at the top, or you can simply '''quit''' if you just wanted to test the authentication.
-−
-−
 ==See Also==

@@ Line 41: / Line 41: @@
 First, we need to generate a base64-encoded string for the PLAIN method, in the form of [null]username[null]password :
-  # '''perl -MMIME::Base64 -e 'print encode_base64("\0user\@domain.com\0password");' '''
+  # '''perl -MMIME::Base64 -e 'print encode_base64("\000user\@domain.com\000password");' '''
   AHVzZXJAZG9tYWluLmNvbQBwYXNzd29yZA==

@@ Line 96: / Line 96: @@
 ==See Also==
 [[Daemons, testing via Telnet]]
 [[IMAP, testing via Telnet]]
 [[POP3, testing via Telnet]]
 [[Category:FreeBSD for Servers]] [[Category:Common Tasks]]