Test SMTP Mail Server With Telnet

Marty (admin) — Fri, 06 Nov 2009 05:24:07 +0000

Testing SMTP with telnet can come in handy. You may have just set up your mailserver and want to test it, or your email client is having problems sending emails and is not giving very helpful error messages (if any). Using telnet is handy as it will throw up any error messages which will help you do understand at what part of the sending process the failure has occured.

Testing with Telnet is real quick and simple,we are going to assume plain password authentication and no TLS or SSL.

We need to open a connection to the server

$ telnet yourmailserver.com 25

You should get a response like this

Trying 74.125.79.16..
Connected to yourmailserver.com.
Escape character is '^]'.
220 mx.yourmailserver.com

Now we need to greet the serer

HELO yourmailserver.com

Response

250 yourmailserver.com

We need to authenticate ourselves with our username and password. This may not be neccessary for all SMTP servers.
We are going to use plain authentication but we need to encode it to base64. Below is two ways to do this with Perl or PHP, with both methods you must leave in the “\0″ characters.
```
$ php -r 'echo base64_encode("\0username\0password")."\n";'
```
or
```
$ perl -MMIME::Base64 -e 'print encode_base64("\0username\0password");'
```
Take the value given and pass it to the mail server
```
AUTH PLAIN AHVzZXJuYW1lAHBhc3N3b3Jk
```
Response
```
235 2.7.0 Authentication successful
```
Now we start to send a test message by putting in who the mail is from
```
MAIL FROM:me@mydomain.com
```
Response
```
250 2.1.0 Ok
```
Add recipient
```
RCPT TO:me@myotheremail.com
```
Response
```
250 2.1.5 Ok
```
Add a subject
```
SUBJECT: Test message from me
```
Start the message
```
DATA
```
Response
```
354 End data with .
```
Press enter then add the message body
```
Hi this is my test message
```
Press enter and on the next line type a “.” then enter
```
.
```
Response
```
250 2.0.0 Ok: queued as 666F4E0157
```
Thats it the message is on the way now quit
```
QUIT
```

Martin Fleming » Troubleshooting

Test SMTP Mail Server With Telnet