You can need to perform testing with your SMTP server and see if you are able to send mail with it.
You have your domain name, and you want to check if mail server is answering properly?
1. Check the mail server with DNS entries
We first need to find the right DNS entry for MX record and know what is the mail server.
~$ nslookup > server 22.214.171.124 Default server: 126.96.36.199 Address: 188.8.131.52#53 > set querytype=MX > mydomain.com Server: 184.108.40.206 Address: 220.127.116.11#53 Non-authoritative answer: mydomain.com mail exchanger = 10 mail.mydomain.com.
2. Open connection to mail server (default ports 25,587)
We will now open a telnet connection on the mail server we just found. Port to use can be different depending on the configuration of the server mail.
~$ telnet mail.mydomain.com 587 Trying www.xxx.yyy.zzz... Connected to mydomain.com. Escape character is '^]'. 220 mail.mydomain.com ESMTP Postfix
The answer can change depending on the mail engine used, this is just an example.
3. Send an email with or without authentication
In case of there is no authentication needs (an open smtp server), just perform:
EHLO mydomain.com 250 MAIL FROM:<[email protected]> 250 OK RCPT TO:<[email protected]> 250 OK DATA 354 GO AHEAD From: Me <[email protected]> To: Him <[email protected]> Subject: This is a testing mail This message is only sent for testing purposes. . 250 OK 1413684421 qp 18534 QUIT 221
If the server requests an SSL/TLS authentication before being able to send mail, you will probably need to use openssl library as telnet does not support TLS by default (you will get an error on STARTTLS command).
You will also need to prepare the credentials by encoding them in base 64:
~$ echo -ne ' user password' | base64 AHVzZXIAcGFzc3dvcmQ=
Once you got this, you can open connection and request mail sending as following:
openssl s_client -starttls smtp -connect mail.mydomain.com:587 CONNECTED(00000003) EHLO mydomain.com 250-mail.mydomain.com 250-PIPELINING 250-SIZE 10240000 250-VRFY 250-ETRN 250-AUTH PLAIN LOGIN 250-AUTH=PLAIN LOGIN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN AUTH PLAIN AHVzZXIAcGFzc3dvcmQ= 235 2.7.0 Authentication successful mail from: <[email protected]> 250 2.1.0 Ok rcpt to: <[email protected]> 250 2.1.5 Ok DATA 354 End data with . From: Me <[email protected]> To: Him <[email protected]> Subject: This is a testing mail This mail is only for testing purposes . 250 2.0.0 Ok: queued as E65832403CF QUIT DONE
Notice that if the mail server doesn’t allow SMTP relay, you won’t be able to send a mail to another domain that the ones that this server is allowing. In that case, you will get an error as:
554 5.7.1 <[email protected]>: Relay access denied
That means you will only be able to send mail to an “@mydomain.com” mail address and not to any other.