1) You need to make sure that your mail relay has sign up for open IP relay and the IP is added to your mail relay account. To check if the IP is there, login to your DNS Exit account (or click on My Account if already login). You should see the mail relay account under "Mail Relay" section. Click either "Manage" or the mail relay name to enter Mail Relay Control Panel. You should see the IP there next to "Open Relay IP addresses".
2) Make sure you are at the IP address by visiting whatismyip.com. Make sure the IP you see at whatismyip.com is the same as the IP you enter to your mail relay open IP.
3) You can test an email to verify that our mail relay system is open relay to your IP by using telnet command:
To verify that our mail relay system is open relay to your IP, you can use telnet command.
Note: Bold text are commands that you should type. Replace the red text with your own content. Blue text are comments.
>> telnet relay.dnsexit.com 25 #may use other ports 25, 26, 940, 80, 587 or 2525
Connected to relay.dnsexit.com (22.214.171.124).
Escape character is '^]'.
220 box20.911domain.com ESMTP Sendmail 8.14.4/8.14.4; Fri, 29 Apr 2016 20:41:55 -0400
250 box20.911domain.com Hello svn [126.96.36.199], pleased to meet you
mail from:<firstname.lastname@example.org> # enter the from email
250 2.1.0 <email@example.com>... Sender ok
rcpt to:<firstname.lastname@example.org> # enter the recipient's email
250 2.1.5 <email@example.com>... Recipient ok
data # type "data" and hit enter
354 Enter mail, end with "." on a line by itself
subject: test email # type the subject
test email. ignore # enter the email content
. # enter a period to indicate end the email
250 2.0.0 u3U0ftkg026733 Message accepted for delivery
quit # enter quit to end sending
221 2.0.0 box20.911domain.com closing connection
Connection closed by foreign host.
The email should get sent to destination. If the IP is not open relayed, after the rcpt to command, you should get the following error:
550 5.7.1 <firstname.lastname@example.org>... Relaying denied. Proper authentication