When starting to troubleshoot smtp issues you can do this easily via telnet, below a hosrt description on how to perform the test:
First we will make connection to the mailserver on port 25.
telnet mail.company.com 25
You will receive the following answer when, for example, you connect to an Exchange server
220 mail.company.com Microsoft ESMTP MAIL Service, Version: 6.0.3790.3959 ready at Sun, 5 Apr 2009 21:36:57 +0200
You will need to reply with a helo followed by the domain you are sending from
Next you will need to specify the sender of the mail
mail from: firstname.lastname@example.org
When the sender has been accepted the mailserver will respond with a 250 – OK
250 2.1.0 OK – Mail FROM email@example.com
Next thing you need to specify is the recipient of the mail
rcpt to: firstname.lastname@example.org
When the recipient address has been excepted the mailserver again will respond with a 250 OK
250 2.1.5 OK recipient email@example.com
Now we have specified both the sender and recipient we can specify the mail, this will be done via the command data
When you have send the aboe command to the mailserver it will respond with the following command
354 Send data. End with CRLF.CRLF
The mailserver will tell you that you will need to end the mail with a .
First we specify the subject of the mail, when you don’t do this the subject will be empty.
subject: smtp test via telnet
After the subject command has been specified you will need to press enter 2 times, you won’t receive feedback of this. The 2 times enter is needed according to RFC-822 and RFC-2822.
Now we have specified the subject we can specify the text we would like to be in the mail
_This mail is send via telnet
As mentioned earlier we end the mail with a ., the . needs to be placed on a new line. When the mail has been accepted by the mailserver for delivery it will respond with the following command
250 2.6.0 COMPANY5Kns1ZEqUz00000001@company.com Queued mail for delivery
To disconnect from the mailserver you will need to use the command quit
For further information of the RFC’s have a look at the sites below.